Display device

ABSTRACT

Provided is a display device with high resolution, high display quality, or high aperture ratio. A pixel includes three subpixels and is electrically connected to two gate lines. One of the gate lines is electrically connected to a gate of a transistor included in each of the two subpixels, and the other gate line is electrically connected to a gate of a transistor included in the other subpixel. Display elements of the three subpixels are arranged in the same direction. Three pixel electrodes of the three subpixels are arranged in the same direction.

TECHNICAL FIELD

One embodiment of the present invention relates to a display device.

Note that one embodiment of the present invention is not limited to theabove technical field. The technical field of one embodiment of theinvention disclosed in this specification and the like relates to anobject, a method, or a manufacturing method. One embodiment of thepresent invention relates to a process, a machine, manufacture, or acomposition of matter. Examples of the technical field of one embodimentof the present invention disclosed in this specification include asemiconductor device, a display device, a light-emitting device, alighting device, a power storage device, a storage device, a method fordriving any of them, and a method for manufacturing any of them.

BACKGROUND ART

In recent years, a high-definition display device has been required. Forexample, full high-definition (the number of pixels is 1920×1080) hasbeen in the mainstream of home-use television devices (also referred toas a television or a television receiver); however, 4K (the number ofpixels is 3840×2160) and 8K (the number of pixels is 7680×4320) willalso be spread with the development of high-definition televisiondevices.

High-definition display panels of portable information terminals, suchas mobile phones, smartphones, and tablets, have also been developed.

Examples of the display device include, typically, a liquid crystaldisplay device, a light-emitting device including a light-emittingelement such as an organic electroluminescent (EL) element or alight-emitting diode (LED), and an electronic paper performing displayby an electrophoretic method or the like.

For example, in a basic structure of an organic EL element, a layercontaining a light-emitting organic compound is provided between a pairof electrodes. By voltage application to this element, thelight-emitting organic compound can emit light. A display deviceincluding such an organic EL element needs no backlight which isnecessary for liquid crystal display devices and the like, and a thin,lightweight, high contrast, and low power consumption display device canbe thus obtained. Patent Document 1, for example, discloses an exampleof a display device using organic EL elements.

REFERENCE Patent Document

[Patent Document 1] Japanese Published Patent Application No.2002-324673

DISCLOSURE OF INVENTION

The area of a display region of a display panel mounted on a portableinformation terminal, for example, is smaller than that of a televisiondevice and the like, and thus the resolution needs to be increased forhigh definition.

An object of one embodiment of the present invention is to provide adisplay device with extremely high resolution. Another object is toprovide a display device with high display quality. Another object is toprovide a display device with high aperture ratio. Another object is toprovide a highly reliable display device. Another object is to provide adisplay device with a novel structure.

Note that the descriptions of these objects do not disturb the existenceof other objects. There is no need to achieve all of these objects withone embodiment of the present invention. Objects other than the aboveobjects will be apparent from and can be derived from the description ofthe specification and the like.

Means for Solving the Problems

One embodiment of the present invention is a display device including apixel, a first wiring, and a second wiring. The pixel includes a firstsubpixel, a second subpixel, and a third subpixel. The first subpixelincludes a first transistor and a first display element. The secondsubpixel includes a second transistor and a second display element. Thethird subpixel includes a third transistor and a third display element.The first wiring is electrically connected to a gate of the firsttransistor and a gate of the second transistor. The second wiring iselectrically connected to a gate of the third transistor.

In the above, the first display element includes a first electrode, thesecond display element includes a second electrode, and the thirddisplay element includes a third electrode. The third electrodepreferably includes a region between the first electrode and the secondelectrode in a plane view.

In the above, a straight line through a centroid of the first electrodeand a centroid of the second electrode does not preferably overlap witha centroid of the third electrode in a plane view.

In the above, it is preferable that the first electrode and the secondwiring do not overlap with each other, the second electrode and thesecond wiring do not overlap with each other, and the third electrodeand the first wiring include an overlap region.

Another embodiment of the present invention is a display deviceincluding a first pixel, a second pixel, a first wiring, and a secondwiring. The first pixel includes a first subpixel, a second subpixel,and a third subpixel. The second pixel includes a fourth subpixel, afifth subpixel, and a sixth subpixel. The first subpixel includes afirst transistor and a first display element. The second subpixelincludes a second transistor and a second display element. The thirdsubpixel includes a third transistor and a third display element. Thefourth subpixel includes a fourth transistor and a fourth displayelement. The fifth subpixel includes a fifth transistor and a fifthdisplay element. The sixth subpixel, includes a sixth transistor and asixth display element. The first wiring is electrically connected to agate of the first transistor, a gate of the second transistor, and agate of the fourth transistor. The second wiring is electricallyconnected to a gate of the third transistor, a gate of the fifthtransistor, and a gate of the sixth transistor.

In the above, it is preferable that the first display element include afirst electrode, the second display element include a second electrode,the third display element include a third electrode, the fourth displayelement include a fourth electrode, the fifth display element include afifth electrode, and the sixth display element include a sixthelectrode. In addition, it is preferable that the third electrodeinclude a region between the first electrode and the second electrode ina plane view, the fourth electrode include a region between the fifthelectrode and the sixth electrode in a plane view, and the secondelectrode be adjacent to the fifth electrode in a plane view.

In the above, it is preferable that a centroid of the first electrode, acentroid of the second electrode, and a centroid of the fourth electrodebe in a first line; a centroid of the third electrode, a centroid of thefifth electrode, and a centroid of the sixth electrode be in a secondline; and the first line be parallel to and do not overlap with thesecond line.

In the above, it is preferable that the first electrode and the secondwiring do not overlap with each other, the second electrode and thesecond wiring do not overlap with each other, the third electrode andthe first wiring include an overlap region, the fourth electrode and thesecond wiring do not overlap with each other, the fifth electrode andthe first wiring include an overlap region, and the sixth electrode andthe first wiring include an overlap region.

In the above, it is preferable that the display device include a thirdwiring, a fourth wiring, and a fifth wiring; one of a source and a drainof the first transistor be electrically connected to the third wiring;one of a source and a drain of the second transistor be electricallyconnected to the fourth wiring; one of a source and a drain of the thirdtransistor be electrically connected to the third wiring; one of asource and a drain of the fourth transistor be electrically connected tothe fifth wiring; one of a source and a drain of the fifth transistor beelectrically connected to the fourth wiring; and one of a source and adrain of the sixth transistor be electrically connected to the fifthwiring.

Alternatively, it is preferable that the display device include thethird wiring, the fourth wiring, the fifth wiring, and a sixth wiring;one of the source and the drain of the first transistor be electricallyconnected to the fourth wiring; one of the source and the drain of thesecond transistor be electrically connected to the fifth wiring; one ofthe source and the drain of the third transistor be electricallyconnected to the third wiring; one of the source and the drain of thefourth transistor be electrically connected to the sixth wiring; one ofthe source and the drain of the fifth transistor be electricallyconnected to the fourth wiring; and one of the source and the drain ofthe sixth transistor be electrically connected to the fifth wiring.

In the above, it is preferable that the fourth wiring be between thesecond electrode and the third electrode and that the fifth wiring bebetween the fourth electrode and the fifth electrode in a plane view.

In the above, it is preferable that the first display element and thefifth display element have a function of emitting light of a firstcolor, the second display element and the sixth display element have afunction of emitting light of a second color, and the third displayelement and the fourth display element have a function of emitting lightof a third color.

In the above, a resolution of the display device is preferably more thanor equal to 400 ppi and less than or equal to 2000 ppi.

In the above, the display device preferably includes a circuit having afunction of selectively outputting current flowing through each of thefirst to third display elements and a function of supplying respectivepredetermined potentials to the first to third display elements.

One embodiment of the present invention can provide a display devicewith extremely high resolution, a display device with high displayquality, a display device with high aperture ratio, a highly reliabledisplay device, or a display device with a novel structure.

Note that the description of these effects does not disturb theexistence of other effects. One embodiment of the present invention doesnot necessarily achieve all the objects listed above. Other effects willbe apparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A, 1B, and 1C illustrate a structure example of a display deviceof one embodiment.

FIG. 2 illustrates a structure example of a display device of oneembodiment.

FIG. 3 illustrates a structure example of a display device of oneembodiment.

FIGS. 4A and 4B illustrate a structure example of a display device ofone embodiment.

FIGS. 5A and 5B illustrate a structure example of a display device ofone embodiment.

FIGS. 6A and 6B illustrate a structure example of a display device ofone embodiment.

FIGS. 7A, 7B, and 7C are circuit diagrams of a display device of oneembodiment.

FIGS. 8A, 8B, 8C, and 8D are circuit diagrams of a display device of oneembodiment.

FIGS. 9A and 9B are circuit diagrams of a display device of oneembodiment.

FIG. 10 is a circuit diagram of a display device of one embodiment.

FIGS. 11A and 11B illustrate a structure example of a display device ofone embodiment.

FIGS. 12A and 12B illustrate a structure example of a display device ofone embodiment.

FIGS. 13A and 13B illustrate a structure example of a display device ofone embodiment.

FIGS. 14A and 14B illustrate a structure example of a display device ofone embodiment.

FIGS. 15A and 15B illustrate a structure example of a display device ofone embodiment.

FIG. 16 illustrates a structure example of a display device of oneembodiment.

FIG. 17 illustrates a structure example of a display device of oneembodiment.

FIG. 18 illustrates a structure example of a display device of oneembodiment.

FIGS. 19A and 19B illustrate a structure example of a touch panel of oneembodiment.

FIGS. 20A and 20B are a block diagram and a timing chart of a touchsensor of one embodiment.

FIG. 21 is a circuit diagram of a touch sensor of one embodiment.

FIGS. 22A, 22B, 22C1, 22C2, 22D, 22E, 22F, 22G, and 22H illustrateexamples of electronic devices and a lighting device of one embodiment.

FIGS. 23A1, 23A2, 23B, 23C, 23D, 23E, 23F, 23G, 23H, and 23I illustratean example of an electronic device of one embodiment.

FIGS. 24A, 24B, 24C, 24D, and 24E illustrate an example of an electronicdevice of one embodiment.

FIGS. 25A, 25B, and 25C illustrate an example of an electronic device ofone embodiment.

FIG. 26 shows electrical characteristics of a transistor of Example 1.

FIGS. 27A and 27B are photographs of a display panel of Example 1.

FIG. 28 shows a structure of a light-emitting element of Example 2.

FIGS. 29A and 29B are chromaticity diagrams of Example 2.

FIG. 30 shows luminance dependence of NTSC ratio of Example 2.

FIG. 31 shows electrical characteristics of a transistor of Example 3.

FIGS. 32A and 32B show luminance dependence of NTSC ratio and achromaticity diagram of Example 3.

FIGS. 33A and 33B show viewing angle dependence of chromaticity ofExample 3.

FIGS. 34A and 34B show viewing angle dependence of chromaticity ofExample 3.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described in detail with reference to drawings. Notethat the present invention is not limited to the description below, andit is easily understood by those skilled in the art that various changesand modifications can be made without departing from the spirit andscope of the present invention. Accordingly, the present inventionshould not be interpreted as being limited to the content of theembodiments below.

Note that in the structures of the invention described below, the sameportions or portions having similar functions are denoted by the samereference numerals in different drawings, and description of suchportions is not repeated. In addition, the same hatching pattern isapplied to portions having similar functions, and the portions are notespecially denoted by reference numerals in some cases.

Note that in each drawing described in this specification, the size, thelayer thickness, or the region of each component is exaggerated forclarity in some cases. Therefore, embodiments of the present inventionare not limited to such a scale.

Note that in this specification and the like, ordinal numbers such as“first”, “second”, and the like are used in order to avoid confusionamong components and do not limit the number.

A transistor is a kind of semiconductor elements and can achieveamplification of current or voltage, switching operation for controllingconduction or non-conduction, or the like. A transistor in thisspecification includes an insulated-gate field effect transistor (IGFET)and a thin film transistor (TFT).

Functions of a “source” and a “drain” are sometimes replaced with eachother when a transistor of opposite polarity is used or when thedirection of flow of current is changed in circuit operation, forexample. Therefore, the terms “source” and “drain” can be used to denotethe drain and the source, respectively, in this specification.

Embodiment 1

In this embodiment, a structure example of a display device of oneembodiment of the present invention is described.

The display device of one embodiment of the present invention includes aplurality of pixels. Each pixel includes a plurality of subpixels. Eachsubpixel includes a display element and a pixel circuit. The displayelements of the subpixels emit different colors. Each pixel circuitincludes at least one transistor. Each display element includes at leastone electrode (also referred to as a pixel electrode) which iselectrically connected to the corresponding pixel circuit. Thetransistor included in each pixel circuit has a function as a switch forselecting the subpixel, and can be referred to as a selectiontransistor. In addition to the selection transistor, an element, such asanother transistor, a capacitor, or a diode, a wiring for connecting theelements, and the like may be included in each pixel circuit.

The display device of one embodiment of the present invention includes aplurality of wirings (also referred to as gate lines) each of which iselectrically connected to a gate of the selection transistor of thepixel circuit. The potential supplied via the wiring controls on/off ofthe selection transistor, thereby controlling selection of the subpixel.

In one embodiment of the present invention, the pixel includes two ormore subpixels. The number of gate lines electrically connected to thepixel is larger than or equal to two and smaller than or equal to thenumber of subpixels per pixel. At least one subpixel of the pixel iselectrically connected to each of the gate lines.

Described here is a configuration example in which the pixel includesthree subpixels and two gate lines are electrically connected to thepixel. Specifically, one gate line is electrically connected to eachgate of the selection transistors of the two subpixels, and the othergate line is electrically connected to a gate of the selectiontransistor of the other subpixel.

Display elements of the three subpixels are arranged in one direction,that is, three pixel electrodes of the three subpixels are arranged inone direction.

Such a pixel structure of the display device of one embodiment of thepresent invention makes it easier to reduce the area occupied by pixels,and accordingly the resolution of the display device can be increased.One reason why the pixel structure can reduce the area occupied bypixels will be explained.

In order to increase the resolution of a display device, the areaoccupied by pixels needs to be reduced by narrowing design rule, such asthe minimum feature size or alignment accuracy between layers, forexample. However, design rule tightening depends on performancecapabilities of the manufacturing apparatus and is very difficult. Forexample, cost of technical development of a light-exposure apparatus isextremely high, and even if a novel manufacturing apparatus isdeveloped, huge cost of capital investment is necessary to replaceexisting apparatus with the novel one.

A comparison example in which one gate line is connected to eachselection transistor of three subpixels is considered. A pixel that issquare or substantially square in planar view is preferable. In thiscase, three pixel circuits are arranged in the extending direction of agate line. In the case of the square pixel, the pixel circuit needs tobe fit at least in a rectangular in which the ratio of the length in theextending direction of a gate line to the length in the directionintersecting with the extending direction is approximately 1:3. Inaddition, in order to reduce area occupied by the pixel that is squarein planar view, not either one of but both of the length in theextending direction of a gate line and the length in the directionintersecting with the extending direction need be reduced to a similarextent.

Because there is design rule for process, the size of an element, anelectrode, and a contact hole which are included in a pixel circuit, thewidth of a wiring between the elements, the distance between theelements, and the distance between the element and the wiring, and thelike are not allowed to be below a certain value in the manufacturingprocess of the pixel circuit It is thus difficult to reduce the lengthof the subpixel on the short side of the rectangle, that is, the lengthof the subpixel on the extending direction of a gate line to a similarextent as the length of the subpixel on the long side of the rectangleby taking any measure to arrange an element, a wiring, and the like sothat the area occupied by the subpixel, which is fit into the rectangle,can be reduced. In addition, one or more wiring intersecting a gate lineneeds to be provided in each pixel circuit. Thus, more components, suchas a wiring, are densely provided in the pixel in the extendingdirection of a gate line than in the direction intersecting with theextending direction. For this reason, it is more difficult to reduce thelength of a pixel circuit in the extending direction of a gate line.

In a pixel of one embodiment of the present invention, the number ofpixel circuits arranged in the extending direction of a gate line can bereduced, which makes it easier to reduce the length of a pixel in theextending direction of the gate line as compared to the above describedstructure. In addition, a wiring intersecting with a gate line can beshared by two pixel circuits that are electrically connected todifferent gate lines in one pixel, which leads to reduction in thenumber of wirings intersecting with a gate line per pixel and makes iteasier to further reduce the length of a pixel in the extendingdirection of a gate line.

One embodiment of the present invention preferably has a structureincluding a pixel unit with a pair of pixels. Specifically, the pixelunit includes a first pixel and a second pixel. In the first pixel, twopixel circuits are connected to a first gate line and one pixel circuitis connected to a second gate line. In the second pixel, one pixelcircuit is connected to the first gate line and two pixel circuits areelectrically connected to the second gate line. Six pixel circuits of apixel unit are preferably arranged to fit in a rectangle in which theratio of the length in the extending direction of a gate line to thelength in the direction intersecting with the gate line is approximately2:1, for example. Such a structure makes it easier to reduce the areaoccupied by the pixel because the pixel circuits can be arranged denselyand efficiently. In addition, the number of wirings intersecting with agate line connected to the pair of pixels can be reduced at least two ascompared to the above comparison structure.

In a display device of one embodiment of the present invention, the areaoccupied by a pixel can be extremely small, and a display deviceincluding an extremely high-resolution pixel portion can be achieved.For example, the resolution of the pixel portion can be more than orequal to 400 ppi (pixels per inch) and less than or equal to 2000 ppi,more than or equal to 500 ppi and less than or equal to 2000 ppi,preferably more than or equal to 600 ppi and less than or equal to 2000ppi, more preferably more than or equal to 800 ppi and less than orequal to 2000 ppi, still more preferably more than or equal to 1000 ppiand less than or equal to 2000 ppi. A 1058 ppi display device can beprovided, for example.

Such a high-resolution display device can be preferably used forelectrical devices which are relatively small, for example, a portableinformation terminal such as a mobile phone, a smartphone, and a tabletterminal, a wearable device such as a smart watch, a finder of a cameraor the like, and displays for medical use.

Structure examples of one embodiment of the present invention aredescribed below.

Structure Example

Structure examples of a display device of one embodiment of the presentinvention are described.

Structure Example of Display Device

FIG. 1A is a schematic top view of a display device 10. The displaydevice 10 includes a pixel portion 11, a circuit 12, a circuit 13, acircuit 14, a terminal portion 15 a, a terminal portion 15 b, aplurality of wirings 16 a, a plurality of wirings 16 b, and a pluralityof wirings 16 c.

The pixel portion 11 includes a plurality of pixels and has a functionof displaying images.

The circuits 12 and 13 each have a function of outputting signals fordriving pixels of the pixel portion 11. For example, the circuits 12 and13 can function as a gate driver circuit and a source driver circuit,respectively.

In the case where, for example, a large number of pixels are provided inthe pixel portion 11, the circuit 13 may be omitted and an ICfunctioning as a source driver circuit may be mounted on the terminalportion 15 a, or a flexible print circuit (FPC) including an IC may beconnected to the terminal portion 15 a. In the case where an IC is used,a circuit for dividing one signal into two or more wirings (e.g., ademultiplexer) is preferably used as the circuit 13 to further reducethe number of terminals of the IC and the FPC, and the definition of thedisplay device 10 can be increased.

The circuit 14 is a circuit (also referred to as a monitor circuit)having a function of selectively outputting current flowing in displayelements of pixels. The circuit 14 may have a function of supplying apredetermined potential to the display elements of the pixels. Thepotentials of signals supplied to the pixels are adjusted depending onthe current output from the circuit 14 to each pixel, and variation inluminance of the pixels in the pixel portion 11 can be compensated.Particularly for the increase in resolution of the pixel portion 11, itis preferable to simplify pixel circuits in pixels to reduce the areaoccupied by the pixels and to compensate variation by a device or acircuit outside the display device 10 (such a method is referred to asan external compensation). Note that the circuit 14 can be omitted inthe case where a pixel circuit has the compensation function (such amethod is referred to as an internal compensation). The circuit 14 mayhave the compensation function.

The terminal portions 15 a and 15 b consist of a plurality of terminals,to which an FPC or an IC can be connected. Each terminal of the terminalportion 15 a is electrically connected to the circuit 13 by the wirings16 a. Some of the terminals of the terminal portion 15 b areelectrically connected to the circuit 12 by the wirings 16 b. Others ofthe terminals of the terminal portion 15 b are electrically connected tothe circuit 14 by the wirings 16 c. Note that the display devices 10 inwhich an FPC or an IC is mounted and is not mounted can be referred toas a display module and a display panel, respectively.

FIG. 1B is a schematic top view showing an arrangement example of pixelelectrodes in the pixel portion 11. The pixel portion 11 includes aplurality of pixel units 20. There are four pixel units 20 in FIG. 1B.Each pixel unit 20 includes pixels 21 a and 21 b. The pixel 21 aincludes pixel electrodes 31 a, 32 a, and 33 a. The pixel 21 b includespixel electrodes 31 b, 32 b, and 33 b. Each pixel electrode serves as anelectrode of a display element, which is described below. A displayregion 22 of each subpixel is inside its pixel electrode.

Six pixel electrodes included in each of the pixel units 20 are arrangedat regular intervals. The pixel electrodes 31 a, 32 a, and 33 a, whichare electrodes of display elements, can emit different colors from eachother. The pixel electrodes 31 b, 32 b, and 33 b can emit the same coloras the pixel electrodes 31 a, 32 a, and 33 a, respectively. Although thethree pixel electrodes with different colors are the same in size in thedrawings, they may differ in size or the display regions 22 may differin size between the pixel electrodes.

For simplicity, symbols R, G, and B for representing electrodes ofdisplay elements that emit red (R), green (G), and blue (B) are added tothe pixel electrodes 31 a, 32 a, and 33 a, respectively. Note that thepixel arrangements shown in FIG. 1B and the like are non-limitingexamples.

FIG. 1C is a circuit diagram showing an arrangement example of pixelcircuits in the pixel portion 11. There are four pixel units 20 in FIG.1C. The pixel 21 a includes pixel circuits 41 a, 42 a, and 43 a. Thepixel 21 b includes pixel circuits 41 b, 42 b, and 43 b. In addition,the pixel portion 11 includes wirings 51 a, 51 b, 52 a, 52 b, 52 c, 53a, 53 b, and 53 c and the like.

The wirings 51 a and 51 b are electrically connected to the circuit 12and have a function as a gate line. The wirings 52 a, 52 b, and 52 c areelectrically connected to the circuit 13 and each have a function as asignal line (also referred to as a data line). The wirings 53 a, 53 b,and 53 c each have a function of supplying a potential to displayelements. Since the display device 10 includes the circuit 14, thewirings 53 a, 53 b, and 53 c are electrically connected to the circuit14.

The pixel circuit 41 a is electrically connected to the wirings 51 a, 52a, and 53 a. The pixel circuit 42 a is electrically connected to thewirings 51 a, 52 b, and 53 b. The pixel circuit 43 a is electricallyconnected to the wirings 51 b, 52 a, and 53 a. The pixel circuit 41 b iselectrically connected to the wirings 51 a, 52 c, and 53 c. The pixelcircuit 42 b is electrically connected to the wirings 51 b, 52 b, and 53b. The pixel circuit 43 b is electrically connected to the wirings 51 b,52 c, and 53 c.

The pixel circuits 41 a, 42 a, 43 a, 41 b, 42 b, and 43 b areelectrically connected to the pixel electrodes 31 a, 32 a, 33 a, 31 b,32 b, and 33 b, respectively. In FIG. 1C, the symbols R, G, and B areput on the pixel circuits for simplicity of correspondence between thepixel circuits and pixel electrodes shown in FIG. 1B.

Although three wirings 52 a to 52 c serving as signal lines areelectrically connected to each pixel unit 20 in FIG. 1C, four wiringsmay be electrically connected to each pixel unit 20 as shown in FIG. 2.

In FIG. 2, a wiring 52 d is electrically connected to the pixel circuit43 a, a wiring 52 a is electrically connected to the pixel circuits 41 aand 42 b, a wiring 52 b is electrically connected to the pixel circuit42 a and the pixel circuit 43 b, and a wiring 52 c is electricallyconnected to the pixel circuit 41 b. Note that the wiring 52 c is sharedby adjacent pixel units and thus the wiring 52 c in the pixel unit 20corresponds to the wiring 52 d in a pixel unit adjacent to the pixelunit 20.

Such a configuration in which a wiring functioning as a signal line isconnected to pixel circuits of the same color is preferable. This isbecause compensation values may differ greatly between colors when asignal whose potential is adjusted to compensate variation in luminancebetween pixels is supplied to the wiring as described above. Thus, itmakes compensation easy to connect pixel circuits with one signal linecolor by color.

In FIG. 2, the number of wirings serving as a signal line (e.g., thewiring 52 a) is n+1 when n is the number of pixel circuits arranged inthe row direction (the extending direction of the wirings 51 a and 51b). Among the wirings serving as a signal line in the pixel portion 11,two wirings at both ends (i.e., the first wiring and the (n+1)-thwiring) are connected to the same-color pixel circuits. In this case,the two wirings at the both ends of the pixel portion 11 (i.e., thewiring 52 d and the wiring 52 c on the right end in FIG. 2) areelectrically connected to each other by a wiring 54 which is outside thepixel portion 11. This is preferable because there is no need toincrease the number of signals output from a circuit functioning as asignal line driver circuit.

Configuration Example of Pixel Circuit

A specific example of a pixel circuit included in the pixel unit 20 isdescribed. FIG. 3 shows an example of a circuit diagram of the pixelunit 20 in which four wirings (the wiring 52 a and the like) functioningas a signal line are connected to one pixel unit 20, which is shown inFIG. 2.

The pixel 21 a includes subpixels 71 a, 72 a, and 73 a. The pixel 21 bincludes subpixels 71 b, 72 b, and 73 b. Each subpixel includes a pixelcircuit and a display element 60. For example, the subpixel 71 aincludes a pixel circuit 41 a and the display element 60. Alight-emitting element such as an organic EL element is used here as thedisplay element 60.

In addition, each pixel circuit includes a transistor 61, a transistor62, and a capacitor 63. In the pixel circuit 41 a, for example, a gateof the transistor 61 is electrically connected to the wiring 51 a, oneof a source and a drain of the transistor 61 is electrically connectedto the wiring 52 a, and the other of the source and the drain iselectrically connected to a gate of the transistor 62 and one electrodeof the capacitor 63. One of a source and a drain of the transistor 62 iselectrically connected to one electrode of the display element 60, andthe other of the source and the drain is electrically connected to theother electrode of the capacitor 63 and the wiring 53 a. The otherelectrode of the display element 60 is electrically connected to awiring to which a potential V1 is applied. Note that the other pixelcircuits similar to the pixel circuit 41 a except that where one of asource and a drain of the transistor 61 and the other electrode of thecapacitor 63 are connected (see FIG. 3).

In FIG. 3, the transistor 61 has a function as a selection transistor.The transistor 62 is in a series connection with the display element 60to control current flowing in the display element 60. The capacitor 63has a function of holding a/the potential of a node connected to thegate of the transistor 62. Note that the capacitor 63 may be omitted inthe case where off-state leakage current of the transistor 61, leakagecurrent through the gate of the transistor 62, and the like areextremely small.

The transistor 62 preferably includes a first gate and a second gateelectrically connected to each other as in FIG. 3. The amount of currentthe transistor 62 can supply can be increased owing to the two gates. Itis particularly preferable for a high-resolution display device becausethe amount of current can be increased without increasing the size, thechannel width in particular, of the transistor 62.

Note that the transistor 62 may have only one gate as in FIG. 4A, inwhich case a step of forming the second gate can be skipped and theprocess can be simpler than the above. In addition, the transistor 61may have two gates as in FIG. 4B, in which case both of the transistors61 and 62 can be reduced in size. In the configurations shown here, thefirst gate and the second gate of each transistor are electricallyconnected to each other, but one of them may be electrically connectedto another wiring. In this case, threshold voltages of the transistorscan be controlled by applying different potentials to the wirings.

The electrode of the display element 60 which is electrically connectedto the transistor 62 corresponds to a pixel electrode (e.g., a pixelelectrode 31 a). In FIG. 3 and FIGS. 4A and 4B, one electrodeelectrically connected to the transistor 62 of the display element 60serves as a cathode and the other serves as an anode, and such astructure is particularly effective when the transistor 62 is ann-channel transistor. When the n-channel transistor 62 is on, thepotential applied from the wiring 53 a is a source potential, and theamount of current flowing in the transistor 62 can be constant withvariation or change in resistance of the display element 60.

Another configuration example shown in FIG. 5A in which the electrode ofthe display element 60 on the transistor 62 side serves as an anode andthe other serves as a cathode may be used. Such a structure allows touse a fixed potential lower than the potential applied to the wiring 53a and the like as the potential V1, which is applied to the otherelectrode of the display element 60. The use of a common potential or aground potential as the potential V1 leads to a simpler circuitconfiguration, which is preferable.

Other than the configuration of FIG. 2, in which one pixel unit isconnected to four wirings serving as a signal line, one pixel unit maybe connected to three wirings serving as a signal line as in FIG. 1C. Inthis case, the pixel unit 20 has a configuration of FIG. 5B, forexample.

Alternatively, a p-channel transistor may be used as a transistor of apixel circuit. FIGS. 6A and 6B show configuration examples in which thetransistors 62 shown in FIGS. 5A and 5B are p-channel transistors.

Monitor Circuit

Next, a structure example of the circuit 14 shown in FIG. 1A isdescribed. FIG. 7A is a circuit diagram of the structure example of thecircuit 14. The circuit 14 includes m (m is an integer greater than orequal to 1) circuits 80: circuits 80_1 to 80_m. A wiring 83, a wiring84, and a plurality of wiring groups 53S are electrically connected tothe circuit 14. The wiring group 53S includes wirings 53 a, 53 b, and 53c at least one or more each. The circuits 14 are electrically connectedto m output terminals 86_1 to 86_m. The output terminals 86 areelectrically connected to respective circuits 80 in the circuit 14.

FIG. 7B illustrates a structure example of the circuit 80. Each circuit80 includes a plurality of transistors 81 and a plurality of transistors82. A gate of the transistor 81 is electrically connected to the wiring83, one of a source and a drain of the transistor 81 is electricallyconnected to one of the wirings of the wiring group 53S, and the otherof the source and the drain is electrically connected to the wiring 84.A gate of the transistor 82 is electrically connected to a terminal 85,one of a source and a drain of the transistor 82 is electricallyconnected to the one of the source and the drain of the transistor 81,and the other of the source and the drain is electrically connected tothe output terminal 86.

A fixed potential, such as a potential higher than the potential V1 or apotential lower than the potential V1, can be applied to the wiring 84.A signal for controlling on/off of the transistor 81 can be applied tothe wiring 83. In a period for displaying images in the pixel portion 11(also referred to as a display period), the transistor 81 is turned onto supply the potential, that is applied to the wiring 84, to the wiringgroup 53S through the transistor 81.

A signal for controlling on/off of the transistor 82 can be applied tothe terminal 85. A non-display period of the pixel portion 11 caninclude a monitor period in which current flowing in each subpixel isoutput to the outside. To output the current in this period, theplurality of transistors 81 are all turned off and one of the pluralityof transistors 82 is turned on, and accordingly any one of the wiringsof the wiring group 53S is electrically connected to the output terminal86 through the transistor 82. Thus, the plurality of transistors 82 aresequentially selected to output current flowing through each wiring ofthe wiring group 53S by time division to the output terminal 86.

Although each transistor 82 shown in FIG. 7B is connected to one wiring(e.g., the wiring 53 a), each transistor 82 is preferably connected to aplurality of adjacent wirings of the wiring group 53S as shown in FIG.7C, in which case the sum of current which is output from the pluralityof pixels is output to the output terminal 86 and accordingly thesensitivity of the display device can be increased. This structure makescompensation easier particularly in such a high-resolution displaydevice in which the size of the display element 60 in each subpixel issmall and the value of current from the display element 60 is alsosmall. In addition, the number of output terminals 86 can be reducedthanks to the united wiring, and the circuit configuration can besimplified.

For example, in the circuit configurations illustrated in FIG. 3, FIGS.4A and 4B, and FIGS. 5A and 5B, the wirings 53 a, 53 b, and 53 c cantransmit current flowing in the display element 60 and the transistor 62to the output terminal 86.

Operation in a monitor period is explained with reference to FIG. 3.Current output from the subpixel 71 a is described as an example. First,a potential is applied to the wiring 51 a to turn the transistor 61 on,and a predetermined potential is applied to the wiring 52 a and a gateof the transistor 62 through the transistor 61. A potential is appliedto other wirings (e.g., the wirings 51 b) serving as a gate line to turntransistors 61 off. A potential is applied to other wirings (e.g., thewirings 52 b) serving as a signal line to turn transistors 62 off. Thisoperation enables current flowing through the display element 60 and thetransistor 62 in the subpixel 71 a to be output to the wiring 53 a.

Note that in the case where a plurality of adjacent wirings of thewiring group 53S is combined into one as shown in FIG. 7C, current flowsat the same time through the display elements 60 of a plurality ofsubpixels in the monitor period. Also at this time, it is preferablethat current be output at the same time only from the same-colorsubpixels in each period.

FIG. 7C shows a structure in which the transistors 81 and 82 eachinclude two gates electrically connected to each other. Such a structureis preferable particularly in the case where a plurality of wirings(e.g., the wiring 53 a) is connected to the transistors 81 and 82because large current needs to flow.

Another structure example of a pixel including the circuit 14 serving asa monitor circuit will be shown.

A subpixel shown in FIG. 8A includes the transistors 61 and 62, thecapacitor 63, and a transistor 64. The subpixel is electricallyconnected to wirings 51, 52, 53, and 55. The wirings 51 and 52 serve asa gate line and a signal line, respectively. The wiring 53 iselectrically connected to the circuit 14. The wiring 55 can supply apredetermined potential or signal.

A gate of the transistor 61 in FIG. 8A is electrically connected to thewiring 51. One of a source and a drain thereof is electrically connectedto the wiring 52, and the other thereof is electrically connected to oneelectrode of the capacitor 63 and a gate of the transistor 62. One of asource and a drain of the transistor 62 is electrically connected to awiring having a function of supplying a potential V2, and the otherthereof is electrically connected to one electrode of the displayelement 60 and one of a source and a drain of the transistor 64. Theother electrode of the capacitor 63 is electrically connected to thewiring 55. A gate of the transistor 64 is electrically connected to thewiring 51, and the other of the source and the drain thereof iselectrically connected to the wiring 53. The other electrode of thedisplay element 60 is electrically connected to a wiring having afunction of supplying the potential V1.

The potential V1 is lower than the potential V2 in the configuration ofFIG. 8A. Note that in the case where an anode and a cathode of thedisplay element 60 are interchanged, the potentials are alsointerchanged.

With the configuration of FIG. 8A, a predetermined potential is appliedto the gate of the transistor 62 to output current flowing in thetransistor 62 to the wiring 53 through the transistor 64. For example,the potential of the wiring 51 is set to turn the transistors 61 and 64on and the potential of the wiring 52 can be used as a potentialsupplied to the gate of the transistor 62.

The gates of the transistors 61 and 64 are electrically connected to thesame wiring, the wiring 51 in FIG. 8A; however, they may be electricallyconnected to different wirings. For example, a wiring 57 is provided toelectrically connect with the gate of the transistor 64 in FIG. 8B. Inthis preferable case, the transistor 64 can remain off during a displayperiod and generation of unintended current in the wiring 53 is thusavoided.

FIG. 8C is different from FIGS. 8A and 8B mainly in that the wiring 55is not provided. In FIG. 8C, the other electrode of the capacitor 63 iselectrically connected to the other of the source and the drain of thetransistor 62, one electrode of the display element 60, and one of thesource and the drain of the transistor 64. Such a structure can reducethe number of wirings and leads to a high-resolution display device.

FIG. 8D shows a configuration in which the gates of the transistors 61and 64 are electrically connected to different wirings, which is similarto the configuration in FIG. 8B.

As already shown, at least one or all of the transistors may have twogates electrically connected to each other, although each transistor hasone gate in FIGS. 8A to 8D. One of the two gates may be electricallyconnected to a wiring for supplying a predetermined potential to controlthreshold voltage of the transistor.

Alternatively, a pixel circuit can have a function of compensatingvariation in threshold voltages of a transistor. FIG. 9A is an exampleof a subpixel including six transistors 93_1 to 93_6, a capacitor 94,and a display element 95. The subpixel is electrically connected towirings 91_1 to 91_5 and wirings 92_1 and 92_2.

FIG. 9B is an example in which a transistor 93_7 is added to thesubpixel shown in FIG. 9A. The subpixel shown in FIG. 9B is electricallyconnected to wirings 91_6 and 91_7. The wirings 91_5 and 91_6 may beelectrically connected to each other.

A subpixel shown in FIG. 10 includes six transistors 98_1 to 98_6, acapacitor 94, and a display element 95 and is electrically connected towirings 96_1 to 96_3 and wirings 97_1 to 97_3. The wirings 96_1 and 96_3may be electrically connected to each other.

Arrangement Example of Pixel Electrode

Next, relative positional relationships between pixel electrodes andwirings are explained.

FIG. 11A is a schematic top view showing an arrangement example of pixelelectrodes and wirings in the pixel portion 11. The wirings 51 a and 52b are alternately arranged. The wirings 52 a, 52 b, and 52 c arearranged in this order to intersect with the wirings 51 a and 51 b. Thepixel electrodes are arranged in the extending direction of the wirings51 a and 51 b.

In the pixel unit 20, the pixel electrodes 31 a and 32 a are providedbetween the wirings 52 c and 52 a; the pixel electrodes 33 a and 31 bare provided between the wirings 52 a and 52 b; and the pixel electrode32 b and 33 b are provided between the wirings 52 b and 52 c. Althoughthe pixel electrodes shown in FIG. 11A do not overlap with theirnext-to-wirings, part of the pixel electrode may overlap with thewiring.

In addition, each pixel electrode in the pixel unit 20 overlaps withboth the wirings 51 a and 51 b serving as a pair of gate lines, in whichcase the area of the pixel electrode can be increased and the apertureratio of the pixel portion can thus be increased.

Arrangement shown in FIG. 11B is preferable; two pixel electrodesbetween a pair of wirings serving as signal lines (e.g., the wirings 52a and 52 b) are shifted from each other in the extending direction ofthe wirings. That is, six pixel electrodes included in each pixel unit20 are alternately arranged in the extending direction of the wiringserving as a gate line.

FIG. 12A shows a positional relationship between the six pixelelectrodes in each pixel unit 20. The mark in each pixel electrode inFIG. 12A denotes a centroid in the plane view, which means a geometriccentroid of the outline of the electrode in the plane view (i.e., atwo-dimensional view of the electrode).

Arrangement shown in FIG. 12A is preferable; a line connecting thecentroid of two pixel electrodes at both ends among three adjacent pixelelectrodes in the extending direction of a wiring serving as a gate linedoes not overlap with the centroid of a pixel electrode between the twopixel electrodes. For example, a straight line 30 a connecting thecentroid of the pixel electrode 31 a with that of the pixel electrode 33a does not overlap with the centroid of the pixel electrode 32 a whichis provided therebetween.

It is preferable that among six pixel electrodes of each pixel unit 20,each centroid of three pixel electrodes be on a first straight line, andeach centroid of the other three pixel electrodes be on a secondstraight line, and that the first straight line and the second straightline be parallel to and do not overlap with each other. For example, thestraight line 30 a connecting each centroid of the pixel electrodes 31a, 33 a, and 32 b is parallel to and does not overlap with a straightline 30 b connecting each centroid of the pixel electrodes 32 a, 31 b,and 33 b.

Note that a line connecting centroids of three or more pixel electrodesis not straight in practice in the case where there is a variation inshapes of the pixel electrodes or in the case where the shapes of thepixel electrodes differ depending on the emission color of pixels. Insuch cases, it can be regarded that the centroids of three or more pixelelectrodes are on a straight line as long as they lie within a band-likerectangle which is horizontally long in the extending direction of awiring serving as a gate line. FIG. 12B shows the case where eachcentroid of the pixel electrodes lie within a band-like rectangle 30 cor 30 d. In this case, the short-side width W of the band-like rectanglecan be less than or equal to 1/10 of the pixel pitch, preferably lessthan or equal to 1/20 of the pixel pitch.

It is preferable here that one pixel electrode be provided so as not tooverlap with more than two wirings serving as a gate line as shown inFIG. 11B. When the potential of the wiring serving as a gate line ischanged, the potential of a pixel electrode overlapping with the wiringis also changed to change voltage applied to a display element in somecases. In addition, if one pixel electrode does not overlap any wiringserving as a gate line, the aperture ratio of the pixel might bedecreased. For these reasons, the structure in which one electrodeoverlaps with one wiring serving as a gate line can reduce the influenceof change in potentials of a pixel electrode and also maintain highaperture ratio.

One pixel includes two gate lines serving as a gate line in oneembodiment of the present invention; thus it is particularly preferablethat adjacent pixel electrodes be shifted to each other and one pixelelectrode overlap with a wiring serving as a gate line and connected toa pixel or a wiring serving as a gate line and connected to the adjacentpixel of the pixel electrode as shown in FIG. 11B. In addition, it ispreferable that a wiring overlapping with a pixel electrode of onesubpixel be a gate line in the previous row in the scanning direction ofgate lines. In which case, if the potential of the pixel electrode ischanged by a signal applied to the gate line in the previous row andvoltage applied to a display element is accordingly changed, data can berewritten immediately after the change; thus, the influence on displaycan be reduced.

Note that in the case where a pixel electrode needs to be provided tooverlap with two gate lines, the overlap area of the pixel electrode andone of the gate lines is smaller than the overlap area of the pixelelectrode and the other of the gate lines. Particularly when thepercentage of the overlap area of the pixel electrode and each gate lineis less than 3%, change in the potential of the gate line has littleinfluence on the potential of the pixel electrode, and thus it can beregarded that they do not overlap with each other.

FIG. 13A shows an arrangement example of the pixel electrodes, which isdifferent from FIGS. 11A and 11B. In the pixel 21 a, the pixelelectrodes 32 a and 33 a are alternately arranged in the extendingdirection of a wiring serving as a gate line (e.g., the wiring 51 a). Inaddition, the pixel electrode 31 a is provided next to both of the pixelelectrodes 32 a and 33 a.

FIG. 13B shows an example in which the pixel electrodes 32 a and 33 a inone pixel and those in a pixel adjacent to the pixel in the extendingdirection of a wiring serving as a signal line (e.g., the wiring 52 a)are provided in reversed positions. That is, in two adjacent pixels, thepixel electrodes 32 a or the pixel electrodes 33 a are adjacent to eachother.

For easy understanding, the symbols R, G, and B are put on the pixelelectrodes and the pixel circuits in the non-limiting examples; however,they can be interchanged with one another.

[Example of Pixel Layout]

A layout example of the pixel unit 20 will be described.

FIGS. 14A and 14B each show a layout example of the pixel unit 20 whichis shown in FIG. 4A. In FIG. 14A, structures in a layer below the pixelelectrode 31 a and the like are shown. In FIG. 14B, the pixel electrode31 a and the like are added to the structures in FIG. 14A. Note thatpixel electrodes and the like of a pixel unit adjacent to the pixel unit20 are not clearly illustrated for simplicity.

In FIG. 14A, the wirings 51 a, 51 b, and the like are formed using afirst conductive film, and the wirings 52 a and the like are formedusing a second conductive film over the first conductive film.

In the subpixel 71 a, the transistor 61 includes a semiconductor layerover the wiring 51 a, part of the wiring 52 a, and the like. Thetransistor 62 includes a conductive layer formed of the first conductivefilm, a semiconductor layer over the conductive layer, the wiring 53 a,and the like. The capacitor 63 includes part of the wiring 53 a and theconductive layer formed of the first conductive film.

Each pixel electrode in FIG. 14B overlaps with part of a subpixeladjacent to the pixel electrode in the extending direction of the wiring52 a and the like. For example, the pixel electrode 32 a overlaps withpart of the transistor 61 and the capacitor 63 which are included in thesubpixel 71 a, a wiring and an electrode which form the subpixel 71 a,and the like. Such a structure is effective particularly in atop-emission light-emitting element. The provision of a circuit below apixel electrode leads to high aperture ratio even when the area occupiedby a pixel is reduced.

In addition, the structure shown in FIG. 14B is preferable in that eachpixel electrode does not overlap with a wiring serving as a signal line,such as the wiring 52 a, in which case the effect of potential change ofthe signal line on the potential of the pixel electrode can besuppressed. Note that in the case where a pixel electrode needs tooverlap with a signal line, the percentage of their overlapping area onthe area of a pixel electrode is 10% or less, preferably 5% or less.

In the case where a pixel electrode overlaps with a semiconductor layerof a transistor of a subpixel adjacent to the pixel electrode, thethreshold voltage of the transistor might be changed with the potentialchange of the pixel electrode. In FIG. 14B, for example, the pixelelectrode 32 a overlaps with a semiconductor layer of the transistor 61which functions as a selection transistor of the subpixel 71 a. It ispreferable here that a pixel electrode overlap with a selectiontransistor of a subpixel in the previous row in the scan direction. Withthis structure, if the potential of the pixel electrode is changed whenthe appropriate subpixel is selected, a subpixel overlapping with andadjacent to the selected one is not selected and accordingly a selectiontransistor of the subpixel adjacent to the selected one remains off. Thepotential can thus be applied to a gate line of the subpixel adjacent tothe selected one so that the selection transistor of the subpixel can beturned off without fail, and driving operation can be performed with noproblem despite some change in the threshold voltage.

FIGS. 15A and 15B show an arrangement example in which the displayregion 22 of each subpixel in a pixel unit is provided between a pair ofwirings serving as gate lines (i.e., the wirings 51 a and 51 b). Such anarrangement can reduce misalignment of two display regions 22 adjacentto each other in the extending direction of a wiring serving as a signalline (e.g., the wiring 52 a). The wirings 51 a and 52 b are placed atirregular intervals in this non-limiting example.

That is the description of the structure examples of the display device.

Cross-Sectional Structure Example

A cross-sectional example of the display device 10 will be shown.

Cross-Sectional Structure Example 1

FIG. 16 is a schematic cross-sectional view of the display device 10.FIG. 16 shows a cross-section taken along the cut line A1-A2 of FIG. 1A.A cross section of the pixel portion 11 is along the cut line B1-B2 ofFIG. 14B.

The display device 10 includes a first substrate 101 and a secondsubstrate 102 bonded with an adhesive layer 220.

Over the first substrate 101, terminal portions 15 a and 15 b, wirings16 a and 16 b, a transistor 251 constituting a circuit 13, a transistor252 constituting a circuit 12, transistors 61 and 62, a capacitor 63,and a display element 60 a constituting the pixel portion 11, insulatinglayers 211, 212, 213, and 214, a spacer 215, and the like are provided.

On the second substrate 102, an insulating layer 221, a light-blockinglayer 231, coloring layers 232 a and 232 b, structures 230 a and 230 b,and the like are provided.

The display element 60 a is provided over the insulating layer 213. Thedisplay element 60 a includes a pixel electrode 31 serving as a firstelectrode, an EL layer 222, and a second electrode 223. An opticaladjustment layer 224 a is between the pixel electrode 31 and the ELlayer 222. The insulating layer 214 covers end portions of the pixelelectrode 31 and the optical adjustment layer 224 a.

FIG. 16 shows an example in which the display element 60 b of a subpixelnext to the subpixel including the display element 60 a overlaps withthe transistor 61 and the like. The display element 60 b includes anoptical adjustment layer 224 b. In the case where light of differentcolors is emitted from the display elements 60 a and 60 b through thecoloring layer 232 a or 232 b, the thickness of the optical adjustmentlayer 224 a preferably differs from that of the optical adjustment layer224 b as shown in FIG. 16. A structure in which one of the opticaladjustment layers 224 a and 224 b is not provided may be used.

The circuits 12 and 13 shown in FIG. 16 include the transistors 252 and251, respectively.

Transistors included in the circuit 12, the circuit 13, and the pixelportion 11 may have the same structure. The transistors included in thecircuit 12 may have the same structure or different structures, and thesame is applied to the circuit 13 and the pixel portion 11.

The display elements 60 a and 60 b in FIG. 16 are top-emissionlight-emitting elements. Light emission from the display elements 60 aand 60 b is extracted through the second substrate 102 side. In such astructure, transistors, capacitors, circuits, and the like can beprovided below the display elements 60 a and 60 b (i.e., on the firstsubstrate 101 side); accordingly, the aperture ratio of the pixelportion 11 can be increased.

The coloring layers 232 a and 232 b overlapping with the displayelements 60 a and 60 b, respectively, are provided on the surface of thesecond substrate 102 on the first substrate 101 side. The light-blockinglayer 231 may be provided in regions where the coloring layers 232 a and232 b are not provided. The light-blocking layer 231 may overlap withthe circuits 12 and 13 as shown in FIG. 16. A light-transmittingovercoat layer may be provided to cover the coloring layers 232 a and232 b and the light-blocking layer 231.

On the second substrate 102, the structure 230 a is provided on aninside region which is surrounded by the adhesive layer 220 as seen fromabove, and the structure 230 b is provided on an outside region which isopposed to the inside region with the adhesive layer 220 interposedtherebetween as shown in the cross-sectional view of FIG. 16. Thestructures 230 a and 230 b have a function of suppressing development ofa crack in the insulating layer 221, the second substrate 102, or thelike at the ends of the second substrate 102. The structures 230 a and230 b in FIG. 16 have stacked-film structures including a film formed ofthe same film as the light-blocking layer 231 and a film formed of thesame film as the coloring layer 232 a. Such a stacked structure of morethan two films can increase the effect of suppressing crack development.Although the structures 230 a and 230 b are on both sides of theadhesive layer 220, only one of them is possible. If there is no fear ofgeneration of cracks (e.g., when the second substrate 102 possesses highstiffness), the structures 230 a and 230 b are not necessarily provided.

The spacer 215 is provided over the insulating layer 214. The spacer 215serves as a gap spacer for preventing an overdecrease in the distancebetween the first substrate 101 and the second substrate 102. The anglebetween the surface where the spacer 215 is formed and at least part ofthe side surface of the spacer 215 is preferably approximately 90°, forexample, preferably more than or equal to 45° and less than or equal to120°, further preferably more than or equal to 60° and less than orequal to 100°, still further preferably more than or equal to 75° andless than or equal to 90°. Since the spacer 215 includes a portion withthe angle, a region of the EL layer 222 with a small thickness can beeasily formed on the side surface of the spacer 215. This can prevent aphenomenon in which current flows through the EL layer 222 which causesunnecessary emission of a display element adjacent to a display elementemitting light. The spacer 215 having such a shape between displayelements is particularly effective in the high-resolution pixel portion11 because the distance between the adjacent display elements isreduced.

The spacer 215 preferably overlaps with a wiring (e.g., the wirings 52and 53) which intersects with a gate line.

A color filter method is employed in the display device 10 of oneembodiment of the present invention. For example, a structure in whichpixels of three colors of red (R), green (G), and blue (B) expresses onecolor can be employed for the coloring layer 232 a or 232 b. Inaddition, the use of a pixel of white (W) or yellow (Y) leads toreduction in power consumption, which is preferable.

Owing to the combination of the coloring layer 232 a and a microcavitystructure using the optical adjustment layer 224 a in the displayelement 60 a, light with high color purity can be extracted from thedisplay device 10, which is one embodiment of the present invention. Thethickness of the optical adjustment layer 224 a may be determineddepending on the color of a subpixel. Some subpixels do not necessarilyhave the optical adjustment layer.

An EL layer that emits white light is preferably used as the EL layer222 of the display element 60 a. The use of such a display element 60 aleads to reduction in cost and increase in yield because there is noneed to separately form the EL layers 222 expressing different colors inthe subpixels, and the high-resolution pixel portion 11 can be easilyformed. Furthermore, the optical adjustment layers with differentthicknesses in the subpixels enable to extract light with a wavelengthsuitable for each subpixel, which increases color purity. Note that theEL layers 222 expressing different colors may be separately formed inthe subpixels, in which case one or both of the optical adjustment layerand the coloring layer are not necessarily provided. In the subpixels,at least only the light-emitting layers of the EL layers 222 areseparately formed while each of the other layers thereof are notnecessarily formed separately.

FIG. 16 shows an example in which an FPC 241 and an FPC 242 areelectrically connected to the terminal portion 15 a and the terminalportion 15 b, respectively, and accordingly the display device 10 ofFIG. 16 can be referred to as a display module. Note that a displaydevice without an FPC and the like can be referred to as a displaypanel.

The terminal portion 15 a is electrically connected to the FPC 241 withthe connection layer 243 therebetween. Similarly, the terminal portion15 b is electrically connected to the FPC 242 with the connection layer243 therebetween.

The terminal portion 15 a shown in FIG. 16 has a stacked structure ofthe wiring 16 a and a conductive layer formed of the same conductivefilm as the pixel electrode 31. Similarly, the terminal portion 15 b hasa stacked structure of the wiring 16 b and the conductive layer. Theterminal portions 15 a and 15 b formed of stacked conductive layers canreduce electric resistance and increase mechanical strength, which ispreferable.

As the connection layer 243, any of various anisotropic conductive films(ACF), anisotropic conductive pastes (ACP), or the like can be used.

An IC 244 in FIG. 16 is mounted on the FPC 241 by a chip on film (COF)method. An IC functioning as a source driver circuit can be used as theIC 244, for example.

A material in which impurities such as water or hydrogen do not easilydiffuse is preferably used for the insulating layer 211 and theinsulating layer 221. That is, the insulating layer 211 and theinsulating layer 221 can each function as a barrier film. This structureenables diffusion of impurities to the light-emitting element 60 a andthe transistors to be effectively suppressed even when a material withmoisture permeability is used for the first substrate 101 and the secondsubstrate 102, leading to a highly reliable display device.

There is a space 250 between the first substrate 101 and the secondsubstrate 102 in FIG. 16, which is a sealed hollow structure. Forexample, the space 250 may be filled with an inert gas, such as nitrogenor argon. The sealing method is not limited thereto and solid sealingmay be used.

Modification Example 1

FIG. 17 is an example in which the structure of a transistor isdifferent from the above.

The transistors 62, 251, and 252 include a conductive layer 253functioning as a second gate electrode. That is, a semiconductor layerin which a channel is formed is provided between two gate electrodes.Such transistors can have higher field-effect mobility and thus havehigher on-state current than other transistors. Consequently, a circuitcapable of high-speed operation can be obtained. Furthermore, the areaoccupied by a circuit portion can be reduced. The use of a transistorhaving high on-state current can reduce signal delay in wirings and cansuppress display unevenness even in a display device in which the numberof wirings is increased in accordance with the increase in size orresolution.

Cross-Sectional Structure Example 2

FIG. 18 is a display device which is suitable for bending of the pixelportion 11.

The display device 10 shown in FIG. 18 includes the first substrate 101and the second substrate 102 bonded with a sealant 260, which is a solidsealing structure. For the sealant 260, a resin such as a polyvinylchloride (PVC) resin, an acrylic resin, a polyimide resin, an epoxyresin, a silicone resin, a polyvinyl butyral (PVB) resin, an ethylenevinyl acetate (EVA) resin, or the like can be used. A drying agent maybe contained in the resin.

An adhesive layer 261 is provided over the first substrate 101. Aninsulating layer 216 is provided over the adhesive layer 261. Atransistor, a display element, and the like are provided over theinsulating layer 216. A material in which impurities such as water orhydrogen do not easily diffuse is preferably used for the insulatinglayer 216 similar to the insulating layers 211 and 221.

An adhesive layer 262 is provided between the second substrate 102 andthe insulating layer 221.

In addition, the insulating layer 213 has an opening in a portion closerto the outer periphery of the first substrate 101 than the pixel portion11 and the circuits 12 and 13. It is preferable to form an opening inthe insulating layer 213 formed using a resin material, for example, soas to surround the pixel portion 11, the circuits 12 and 13, and thelike. In such a structure, the vicinity of the side surface of theinsulating layer 213 which is in contact with the outside of the displaydevice 10 does not form a continuous layer with the region overlappingwith the pixel portion 11, the circuits 12 and 13, and the like, so thatdiffusion of impurities, such as water and hydrogen, from the outsidethrough the insulating layer 213 can be suppressed.

The solid sealing structure shown in FIG. 18 makes it easier to keep thedistance between the first substrate 101 and the second substrate 102constant, and flexible substrates can be preferably used as the firstsubstrate 101 and the second substrate 102 so that part or whole of thepixel portion 11 can be bent. For example, the display device 10 isbonded to a curved surface or the pixel portion of the display device 10can be foldable to produce a variety of electronic devices.

The above is the description of the modification example.

Components

The components are described below.

A substrate having a flat surface can be used as the substrate includedin the display device. The substrate on the side from which light fromthe light-emitting element is extracted is formed using a material whichtransmits the light. For example, a material such as glass, quartz,ceramics, sapphire, or an organic resin can be used.

The weight and thickness of the display device can be decreased by usinga thin substrate. Furthermore, a flexible display device can be obtainedby using a substrate that is thin enough to have flexibility.

Examples of glass include alkali-free glass, barium borosilicate glass,and aluminoborosilicate glass.

Examples of a material that has flexibility and transmits visible lightinclude flexible glass, polyester resins such as polyethyleneterephthalate (PET) and polyethylene naphthalate (PEN), apolyacrylonitrile resin, a polyimide resin, a polymethyl methacrylateresin, a polycarbonate (PC) resin, a polyethersulfone (PES) resin, apolyamide resin, a cycloolefin resin, a polystyrene resin, a polyamideimide resin, a polyvinyl chloride resin, and a polytetrafluoroethylene(FIFE). In particular, a material whose thermal expansion coefficient islow is preferred, and for example, a polyamide imide resin, a polyimideresin, or PET can be suitably used. A substrate in which a glass fiberis impregnated with an organic resin or a substrate whose thermalexpansion coefficient is reduced by mixing an organic resin with aninorganic filler can also be used. A substrate using such a material islightweight, and a display device using this substrate can also belightweight accordingly.

Since the substrate through which light emission is not extracted doesnot need to have a light-transmitting property, a metal substrate usinga metal material or an alloy material or the like can be used as well asthe above-described substrates. A metal material and an alloy material,which have high thermal conductivity, are preferably used, in which caseheat can be conducted to the whole substrate, so that a localtemperature rise in the display device can be prevented. To obtainflexibility and bendability, the thickness of a metal substrate ispreferably greater than or equal to 10 μm and less than or equal to 200μm, more preferably greater than or equal to 20 μm and less than orequal to 50 μm.

Although there is no particular limitation on a material of the metalsubstrate, it is preferable to use, for example, aluminum, copper,nickel, a metal alloy such as an aluminum alloy or stainless steel.

It is preferable to use a substrate subjected to insulation treatment insuch a manner that a surface of the conductive substrate is oxidized oran insulating film is formed on the surface. An insulating film may beformed by, for example, a coating method such as a spin-coating methodor a dipping method, an electrodeposition method, an evaporation method,or a sputtering method. An oxide film may be formed on the substratesurface by exposure to or heating in an oxygen atmosphere or by ananodic oxidation method or the like.

The flexible substrate may have a stacked structure of a layer of any ofthe above-mentioned materials and a hard coat layer (e.g., a siliconnitride layer) that protects a surface of the display device from damageor the like, a layer (e.g., an aramid resin layer) that can dispersepressure, or the like. Furthermore, to suppress a decrease in thelifetime of the light-emitting element due to moisture and the like, aninsulating film with low water permeability may be provided. Forexample, a film containing nitrogen and silicon (e.g., a silicon nitridefilm, a silicon oxynitride film) or a film containing nitrogen andaluminum (e.g., an aluminum nitride film) may be provided.

The substrate may be formed by stacking a plurality of layers. When aglass layer is used, a barrier property against water and oxygen can beimproved and thus a reliable display device can be provided.

A substrate in which a glass layer, an adhesive layer, and an organicresin layer are stacked from the side closer to a light-emitting elementcan be used. The thickness of the glass layer is greater than or equalto 20 μm and less than or equal to 200 μm, preferably greater than orequal to 25 μm and less than or equal to 100 μm. With such a thickness,the glass layer can have both a high barrier property against water andoxygen and a high flexibility. The thickness of the organic resin layeris greater than or equal to 10 μm and less than or equal to 200 μm,preferably greater than or equal to 20 μm and less than or equal to 50μm. With such an organic resin layer provided on an outer side of theglass layer, breakage or a crack of the glass layer can be inhibited,resulting in increased mechanical strength. With the substrate thatincludes such a composite material of a glass material and an organicresin, a highly reliable and flexible display device can be provided.

The transistor in the display device 10 includes a conductive layerfunctioning as the gate electrode, the semiconductor layer, a conductivelayer functioning as the source electrode, a conductive layerfunctioning as the drain electrode, and an insulating layer functioningas a gate insulating layer. FIG. 16 shows the case where a bottom-gatetransistor is used.

Note that there is no particular limitation on the structure of thetransistor included in the display device of one embodiment of thepresent invention. For example, a forward staggered transistor or aninverted staggered transistor may be used. A top-gate transistor or abottom-gate transistor may be used. A semiconductor material used forthe transistor is not particularly limited, and for example, an oxidesemiconductor, silicon, or germanium can be used.

There is no particular limitation on the crystallinity of asemiconductor material used for the transistor, and an amorphoussemiconductor or a semiconductor having crystallinity (amicrocrystalline semiconductor, a polycrystalline semiconductor, asingle-crystal semiconductor, or a semiconductor partly includingcrystal regions) may be used. It is preferable that a semiconductorhaving crystallinity be used, in which case deterioration of thetransistor characteristics can be suppressed.

As a semiconductor material for the semiconductor layer of thetransistor, an element of Group 14, a compound semiconductor, or anoxide semiconductor can be used, for example. Typically, a semiconductorcontaining silicon, a semiconductor containing gallium arsenide, anoxide semiconductor containing indium, or the like can be used.

An oxide semiconductor is preferably used as a semiconductor in which achannel of a transistor is formed. In particular, an oxide semiconductorhaving a wider band gap than silicon is preferably used. A semiconductormaterial having a wider band gap and a lower carrier density thansilicon is preferably used because off-state leakage current of thetransistor can be reduced.

The oxide semiconductor preferably contains at least indium (In) or zinc(Zn). The semiconductor layer more preferably contains an In-M-Zn-basedoxide (M is a metal such as Al, Ti, Ga, Ge, Y, Zr, Sn, La, Ce, or Hf).

As the semiconductor layer, it is particularly preferable to use anoxide semiconductor layer including a plurality of crystal parts whosec-axes are aligned perpendicular to a surface on which the semiconductorlayer is formed or the top surface of the semiconductor layer and inwhich the adjacent crystal parts have no grain boundary.

Because such an oxide semiconductor contains no grain boundary,generation of a crack caused by stress when a display panel is bent isprevented. Therefore, such an oxide semiconductor can be preferably usedfor a flexible touch panel which is used in a bent state, or the like.

Such an oxide semiconductor is resistant to etching and thus has a highetching selectivity to a conductive film, for example, which is anadvantage. Thus, the use of such an oxide semiconductor makes it easierto form a channel-etched transistor. This is more suitable forimprovement in resolution than a channel protective transistor becausethe number of fabrication steps and the occupation area can be reducedas compared with those of a channel protective transistor.

Moreover, the use of such an oxide semiconductor for the semiconductorlayer makes it possible to provide a highly reliable transistor in whicha change in the electrical characteristics is suppressed.

Charge accumulated in a capacitor through a transistor can be held for along time because of the low off-state current of the transistor. Whensuch a transistor is used for a pixel, operation of a driver circuit canbe stopped while a gray scale of an image displayed in each displayregion is maintained. As a result, a display device with an extremelylow power consumption can be obtained.

For stable characteristics of the transistor, a base film is preferablyprovided. The base film can be formed with an inorganic insulating filmsuch as a silicon oxide film, a silicon nitride film, a siliconoxynitride film, or a silicon nitride oxide film to have a single-layerstructure or a stacked-layer structure. The base film can be formed by asputtering method, a chemical vapor deposition (CVD) method (e.g., aplasma CVD method, a thermal CVD method, or a metal organic CVD (MOCVD)method), an atomic layer deposition (ALD) method, a coating method, aprinting method, or the like. Note that the base film is not necessarilyprovided if not necessary.

Alternatively, silicon is preferably used as a semiconductor in which achannel of a transistor is formed. Although amorphous silicon may beused as silicon, silicon having crystallinity is particularlypreferable. For example, microcrystalline silicon, polycrystallinesilicon, single crystal silicon, or the like is preferably used. Inparticular, polycrystalline silicon can be formed at a lower temperaturethan single crystal silicon and has higher field effect mobility andhigher reliability than amorphous silicon. When such a polycrystallinesemiconductor is used for a pixel, the aperture ratio of the pixel canbe improved. Even in the case where pixels are provided at extremelyhigh resolution, a gate driver circuit and a source driver circuit canbe formed over a substrate over which the pixels are formed, and thenumber of components of an electronic device can be reduced.

As conductive layers such as a gate, a source, and a drain of thetransistor and a wiring and an electrode in the touch panel, asingle-layer structure or a stacked-layer structure using any of metalssuch as aluminum, titanium, chromium, nickel, copper, yttrium,zirconium, molybdenum, silver, tantalum, and tungsten, or an alloycontaining any of these metals as its main component can be used. Forexample, a single-layer structure of an aluminum film containingsilicon, a two-layer structure in which an aluminum film is stacked overa titanium film, a two-layer structure in which an aluminum film isstacked over a tungsten film, a two-layer structure in which a copperfilm is stacked over a copper-magnesium-aluminum alloy film, a two-layerstructure in which a copper film is stacked over a titanium film, atwo-layer structure in which a copper film is stacked over a tungstenfilm, a three-layer structure in which a titanium film or a titaniumnitride film, an aluminum film or a copper film, and a titanium film ora titanium nitride film are stacked in this order, a three-layerstructure in which a molybdenum film or a molybdenum nitride film, analuminum film or a copper film, and a molybdenum film or a molybdenumnitride film are stacked in this order, and the like can be given. Notethat a transparent conductive material containing indium oxide, tinoxide, or zinc oxide may be used. Copper containing manganese ispreferably used because controllability of a shape by etching isincreased.

As a light-transmitting conductive material, a conductive oxide such asindium oxide, indium tin oxide, indium zinc oxide, zinc oxide, or zincoxide to which gallium is added, or graphene can be used. Alternatively,a metal material such as gold, silver, platinum, magnesium, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, ortitanium, or an alloy material containing any of these metal materialscan be used. Alternatively, a nitride of the metal material (e.g.,titanium nitride) or the like may be used. In the case of using themetal material or the alloy material (or the nitride thereof), thethickness is set small enough to be able to transmit light.Alternatively, a stack of any of the above materials can be used as theconductive layer. For example, a stack of indium tin oxide and an alloyof silver and magnesium is preferably used because the conductivity canbe increased.

Examples of an insulating material that can be used for the insulatinglayers, the spacer 215, and the like include a resin such as acrylic orepoxy resin, a resin having a siloxane bond, and an inorganic insulatingmaterial such as silicon oxide, silicon oxynitride, silicon nitrideoxide, silicon nitride, or aluminum oxide.

As described above, the light-emitting element is preferably providedbetween a pair of insulating films with low water permeability. Thus,impurities such as water can be prevented from entering thelight-emitting element, leading to prevention of a decrease in thereliability of the light-emitting device.

As an insulating film with low water permeability, a film containingnitrogen and silicon (e.g., a silicon nitride film or a silicon nitrideoxide film), a film containing nitrogen and aluminum (e.g., an aluminumnitride film), or the like can be used. Alternatively, a silicon oxidefilm, a silicon oxynitride film, an aluminum oxide film, or the like canbe used.

For example, the water vapor transmittance of the insulating film withlow water permeability is lower than or equal to 1×10⁻⁵ [g/(m²·day)],preferably lower than or equal to 1×10⁻⁶ [g/(m²·day)], furtherpreferably lower than or equal to 1×10⁻⁷ [g/(m²·day)], still furtherpreferably lower than or equal to 1×10⁻⁸ [g/(m²·day)].

As the adhesive layer or the sealing layer, a variety of curableadhesives such as a reactive curable adhesive, a thermosetting adhesive,an anaerobic adhesive, and a photo curable adhesive such as anultraviolet curable adhesive can be used. Examples of these adhesivesinclude an epoxy resin, an acrylic resin, a silicone resin, a phenolresin, a polyimide resin, an imide resin, a polyvinyl chloride (PVC)resin, a polyvinyl butyral (PVB) resin, and an ethylene vinyl acetate(EVA) resin. In particular, a material with low moisture permeability,such as an epoxy resin, is preferred. Alternatively, atwo-component-mixture-type resin may be used. Further alternatively, anadhesive sheet or the like may be used.

Further, the resin may include a drying agent. For example, a substancethat adsorbs moisture by chemical adsorption, such as oxide of analkaline earth metal (e.g., calcium oxide or barium oxide), can be used.Alternatively, a substance that adsorbs moisture by physical adsorption,such as zeolite or silica gel, may be used. The drying agent ispreferably included because it can prevent an impurity such as moisturefrom entering the functional element, thereby improving the reliabilityof the light-emitting device.

In addition, it is preferable to mix a filler with a high refractiveindex or light-scattering member into the resin, in which case theefficiency of light extraction from the light-emitting element can beimproved. For example, titanium oxide, barium oxide, zeolite, zirconium,or the like can be used.

As the light-emitting element, a self-luminous element can be used, andan element whose luminance is controlled by current or voltage isincluded in the category of the light-emitting element. For example, alight-emitting diode (LED), an organic EL element, an inorganic ELelement, or the like can be used.

The light-emitting element may be a top emission, bottom emission, ordual emission light-emitting element. A conductive film that transmitsvisible light is used as the electrode through which light is extracted.A conductive film that reflects visible light is preferably used as theelectrode through which light is not extracted.

The EL layer 222 includes at least a light-emitting layer. In additionto the light-emitting layer, the EL layer 222 may further include one ormore layers containing any of a substance with a high hole-injectionproperty, a substance with a high hole-transport property, ahole-blocking material, a substance with a high electron-transportproperty, a substance with a high electron-injection property, asubstance with a bipolar property (a substance with a high electron- andhole-transport property), and the like.

For the EL layer 222, either a low molecular compound or a highmolecular compound can be used, and an inorganic compound may be used.Each of the layers included in the EL layer 222 can be formed by any ofthe following methods: an evaporation method (including a vacuumevaporation method), a transfer method, a printing method, an inkjetmethod, a coating method, and the like.

In the case where the light-emitting element has a top emissionstructure, a conductive film that transmits visible light is used for anupper electrode, and a conductive film that reflects visible light ispreferably used for a lower electrode. Alternatively, a film of a metalmaterial such as gold, silver, platinum, magnesium, nickel, tungsten,chromium, molybdenum, iron, cobalt, copper, palladium, or titanium; analloy containing any of these metal materials; or a nitride of any ofthese metal materials (e.g., titanium nitride) can be formed thin so asto have a light-transmitting property. Alternatively, a stack of any ofthe above materials can be used as the conductive layer. For example, astacked film of ITO and an alloy of silver and magnesium is preferablyused, in which case conductivity can be increased. Furtheralternatively, graphene or the like may be used.

For the conductive film that reflects visible light, for example, ametal material, such as aluminum, gold, platinum, silver, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, or palladium or analloy including any of these metal materials can be used. Lanthanum,neodymium, germanium, or the like may be added to the metal material orthe alloy. Furthermore, an alloy containing aluminum (an aluminum alloy)such as an alloy of aluminum and titanium, an alloy of aluminum andnickel, or an alloy of aluminum and neodymium; or an alloy containingsilver such as an alloy of silver and copper, an alloy of silver,copper, and palladium, or an alloy of silver and magnesium can be usedfor the conductive film. An alloy of silver and copper is preferablebecause of its high heat resistance. Moreover, a metal film or a metaloxide film is stacked on an aluminum alloy film, whereby oxidation ofthe aluminum alloy film can be suppressed. Examples of a material forthe metal film or the metal oxide film are titanium and titanium oxide.Alternatively, the conductive film having a property of property oftransmitting visible light and a film containing any of the above metalmaterials may be stacked. For example, a stacked film of silver and ITOor a stacked film of an alloy of silver and magnesium and ITO can beused.

The electrodes may be formed separately by an evaporation method or asputtering method. Alternatively, a discharging method such as anink-jet method, a printing method such as a screen printing method, or aplating method may be used.

When a voltage higher than the threshold voltage of the light-emittingelement is applied between the anode and the cathode, holes are injectedto the EL layer from the anode side and electrons are injected to the ELlayer from the cathode side. The injected electrons and holes arerecombined in the EL layer, so that a light-emitting substance containedin the EL layer emits light.

In the case where a light-emitting element emitting white light is usedas the light-emitting element, the EL layer preferably contains two ormore kinds of light-emitting substances. For example, light-emittingsubstances are selected so that two or more light-emitting substancesemit complementary colors to obtain white light emission. Specifically,it is preferable to contain two or more selected from light-emittingsubstances emitting light of red (R), green (G), blue (B), yellow (Y),orange (O), and the like and light-emitting substances emitting lightcontaining two or more of spectral components of R, G, and B. Thelight-emitting element preferably emits light with a spectrum having twoor more peaks in the wavelength range of a visible light region (e.g.,350 nm to 750 nm). An emission spectrum of a material emitting lighthaving a peak in the wavelength range of a yellow light preferablyincludes spectral components also in the wavelength range of a greenlight and a red light.

More preferably, a light-emitting layer containing a light-emittingmaterial emitting light of one color and a light-emitting layercontaining a light-emitting material emitting light of another color arestacked in the EL layer. For example, the plurality of light-emittinglayers in the EL layer may be stacked in contact with each other or maybe stacked with a separation layer therebetween. For example, aseparation layer may be provided between a fluorescent layer and aphosphorescent layer.

The separation layer can be provided to prevent an energy transfer bythe Dexter mechanism (particularly triplet energy transfer) from aphosphorescent material or the like in an excited state which isgenerated in the phosphorescent layer to a fluorescent material or thelike in the fluorescent layer. The thickness of the separation layer maybe approximately several nanometers, specifically 0.1 nm or more and 20nm or less, 1 nm or more and 10 nm or less, or 1 nm or more and 5 nm orless. The separation layer contains a single material (preferably abipolar material) or a plurality of materials (preferably, ahole-transport material and an electron-transport material).

The separation layer may be formed using a material contained in thelight-emitting layer in contact with the separation layer. Thisfacilitates the manufacture of the light-emitting element and reducesthe drive voltage. For example; in the case where the phosphorescentlayer contains a host material, an assist material, and thephosphorescent material (a guest material), the separation layer maycontain the host material and the assist material. In other words, theseparation layer includes a region which does not contain thephosphorescent material, while the phosphorescent layer includes aregion containing the phosphorescent material. Thus, the separationlayer and the phosphorescent layer can be separately deposited dependingon the presence of the phosphorescent material. Furthermore, such astructure enables the separation layer and the phosphorescent layer tobe deposited in the same chamber, which leads to a reduction inmanufacturing cost.

The light-emitting element may be a single element including one ELlayer or a tandem element in which a plurality of EL layers are stackedwith a charge generation layer therebetween.

As examples of a material that can be used for the light-blocking layer231, carbon black, a metal oxide, and a composite oxide containing asolid solution of a plurality of metal oxides can be given.

As examples of a material that can be used for the coloring layer 232 aand the like, a metal material, a resin material, and a resin materialcontaining a pigment or dye can be given.

Manufacturing Method Example

Here, a method for manufacturing a display device is described.

For convenience, a structure including a pixel and a circuit, or astructure including an optical member such as a color filter is referredto as an element layer. An element layer includes a display element, forexample, and may include a wiring electrically connected to the displayelement or an element such as a transistor used in a pixel or a circuitin addition to the display element.

Here, a support body (e.g., the first substrate 101 or the secondsubstrate 102) with an insulating surface where an element layer isformed is referred to as a substrate.

As a method for forming an element layer over a flexible substrateprovided with an insulating surface, there are a method in which anelement layer is formed directly over a substrate, and a method in whichan element layer is formed over a supporting base material that hasstiffness and then the element layer is separated from the supportingbase material and transferred to the substrate.

In the case where a material of the substrate can withstand heatingtemperature in a process for forming the element layer, it is preferablethat the element layer be formed directly over the substrate, in whichcase a manufacturing process can be simplified. At this time, theelement layer is preferably formed in a state where the substrate isfixed to the supporting base material, in which case transfer thereof inan apparatus and between apparatuses can be easy.

In the case of employing the method in which the element layer is formedover the supporting base material and then transferred to the substrate,first, a separation layer and an insulating layer are stacked over thesupporting base material, and then the element layer is formed over theinsulating layer. Next, the element layer is separated from thesupporting base material and then transferred to the substrate. At thistime, a material is selected that would causes separation at aninterface between the supporting base material and the separation layer,at an interface between the separation layer and the insulating layer,or in the separation layer.

For example, it is preferable that a stacked layer of a layer includinga high-melting-point metal material, such as tungsten, and a layerincluding an oxide of the metal material be used as the insulating layerover the separation layer, and a stacked layer of a plurality of layers,such as a silicon nitride layer and a silicon oxynitride layer be usedover the separation layer. The use of the high-melting-point metalmaterial is preferable because the degree of freedom of the process forforming the element layer can be increased.

The separation may be performed by application of mechanical power, byetching of the separation layer, by dripping of a liquid into part ofthe separation interface to penetrate the entire separation interface,or the like. Alternatively, separation may be performed by heating theseparation interface by utilizing a difference in thermal expansioncoefficient.

The peeling layer is not necessarily provided in the case where peelingcan occur at an interface between the supporting base material and theinsulating layer. For example, glass may be used as the supporting basematerial, an organic resin such as polyimide may be used as theinsulating layer, a separation trigger may be formed by locally heatingpart of the organic resin by laser light or the like, and peeling may beperformed at an interface between the glass and the insulating layer.Alternatively, a metal layer may be provided between the supporting basematerial and the insulating layer formed of an organic resin, andseparation may be performed at the interface between the metal layer andthe insulating layer by heating the metal layer by feeding a current tothe metal layer. A layer of a light-absorbing material (e.g., a metal, asemiconductor, or an insulator) may be provided between the supportingbase layer and the insulating layer formed of an organic resin andlocally heated with laser light or the like to form a separationtrigger. In these methods, the insulating layer formed of an organicresin can be used as a substrate.

Examples of such a substrate having flexibility include polyester resinssuch as polyethylene terephthalate (PET) and polyethylene naphthalate(PEN), a polyacrylonitrile resin, a polyimide resin, a polymethylmethacrylate resin, a polycarbonate (PC) resin, a polyethersulfone (PES)resin, a polyamide resin, a cycloolefin resin, a polystyrene resin, apolyamide imide resin, and a polyvinyl chloride resin. In particular, itis preferable to use a material with a low thermal expansioncoefficient, and for example, a polyamide imide resin, a polyimideresin, PET, or the like with a thermal expansion coefficient lower thanor equal to 30×10⁻⁶/K can be suitably used. A substrate in which afibrous body is impregnated with a resin (also referred to as prepreg)or a substrate whose thermal expansion coefficient is reduced by mixingan inorganic filler with an organic resin can also be used.

In the case where a fibrous body is included in the above material, ahigh-strength fiber of an organic compound or an inorganic compound isused as the fibrous body. The high-strength fiber is specifically afiber with a high tensile elastic modulus or a fiber with a high Young'smodulus. Typical examples thereof include a polyvinyl alcohol basedfiber, a polyester based fiber, a polyamide based fiber, a polyethylenebased fiber, an aramid based fiber, a polyparaphenylene benzobisoxazolefiber, a glass fiber, and a carbon fiber. As the glass fiber, glassfiber using E glass, S glass, D glass, Q glass, or the like can be used.These fibers may be used in a state of a woven fabric or a nonwovenfabric, and a structure body in which this fibrous body is impregnatedwith a resin and the resin is cured may be used as the flexiblesubstrate. The structure body including the fibrous body and the resinis preferably used as the flexible substrate, in which case thereliability against bending or breaking due to local pressure can beincreased.

Alternatively, glass, metal, or the like that is thin enough to haveflexibility can be used as the substrate. Alternatively, a compositematerial where glass and a resin material are attached to each other maybe used.

In the structure shown in FIG. 18, for example, a first separation layerand the insulating layer 216 are formed in this order over a firstsupporting base material, and then components in a layer over the firstseparation layer and the insulating layer 216 are formed. Separately, asecond separation layer and the insulating layer 221 are formed in thisorder over a second supporting base material, and then upper componentsare formed. Next, the first supporting base material and the secondsupporting base material are bonded to each other using the sealant 260.After that, separation at an interface between the second separationlayer and the insulating layer 221 is conducted so that the secondsupporting base material and the second separation layer are removed,and then the second substrate 102 is bonded to the insulating layer 221using the adhesive layer 262. Further, separation at an interfacebetween the first separation layer and the insulating layer 216 isconducted so that the first supporting base material and the firstseparation layer are removed, and then the first substrate 101 is bondedto the insulating layer 216 using the adhesive layer 261. Note thateither side may be subjected to separation and attachment first.

The above is the description of a manufacturing method of a flexibledisplay device.

The above is the description of the components.

Note that although the case where the light-emitting element is used asa display element is described here, one embodiment of the presentinvention is not limited thereto.

In this specification and the like, for example, a display element, adisplay device or a display panel which is a device including a displayelement, a light-emitting element, and a light-emitting device which isa device including a light-emitting element can employ a variety ofmodes or can include a variety of elements. The display element, thedisplay device, the display panel, the light-emitting element, or thelight-emitting device includes at least one of an electroluminescence(EL) element (e.g., an EL element containing organic and inorganicmaterials, an organic EL element, or an inorganic EL element), an LED(e.g., a white LED, a red LED, a green LED, or a blue LED), a transistor(a transistor that emits light depending on current), an electronemitter, a liquid crystal element, electronic ink, an electrophoreticelement, a grating light valve (GLV), a plasma display panel (PDP), adisplay element using micro electro mechanical system (MEMS), a digitalmicromirror device (DMD), a digital micro shutter (DMS), MIRASOL(registered trademark), an interferometric modulator display (IMOD)element, a MEMS shutter display element, an optical-interference-typeMEMS display element, an electrowetting element, a piezoelectric ceramicdisplay, a display device including a carbon nanotube, and the like.Other than the above, display media whose contrast, luminance,reflectivity, transmittance, or the like is changed by electrical ormagnetic effect may be included. Note that examples of display deviceshaving EL elements include an EL display. Examples of display devicesincluding electron emitters are a field emission display (FED) and anSED-type flat panel display (SED: surface-conduction electron-emitterdisplay). Examples of display devices including liquid crystal elementsinclude a liquid crystal display (e.g., a transmissive liquid crystaldisplay, a transflective liquid crystal display, a reflective liquidcrystal display, a direct-view liquid crystal display, or a projectionliquid crystal display). Examples of a display device includingelectronic ink, Electronic Liquid Powder (registered trademark), or anelectrophoretic element include electronic paper. In the case of atransflective liquid crystal display or a reflective liquid crystaldisplay, some of or all of pixel electrodes function as reflectiveelectrodes. For example, some or all of pixel electrodes are formed tocontain aluminum, silver, or the like. For example, some or all of pixelelectrodes are formed to contain aluminum, silver, or the like. In sucha case, a memory circuit such as an SRAM can be provided under thereflective electrodes, leading to lower power consumption. Note that inthe case of using an LED, graphene or graphite may be provided under anelectrode or a nitride semiconductor of the LED. Graphene or graphitemay be a multilayer film in which a plurality of layers are stacked. Asdescribed above, provision of graphene or graphite enables easyformation of a nitride semiconductor film thereover, such as an n-typeGaN semiconductor layer including crystals. Furthermore, a p-type GaNsemiconductor layer including crystals or the like can be providedthereover, and thus the LED can be formed. Note that an AlN layer may beprovided between the n-type GaN semiconductor layer including crystalsand graphene or graphite. The GaN semiconductor layers included in theLED may be formed by MOCVD. Note that when the graphene is provided, theGaN semiconductor layers included in the LED can also be formed by asputtering method.

Note that one embodiment of the present invention is not limited to theabove technical field. Non-limiting examples of one embodiment of thepresent invention are described: a structure in which a pixel includestwo or more subpixels and is electrically connected to two or more gatelines; a structure in which one pixel includes a plurality of subpixelswhich is connected to different gate lines; and the like. As anotherexample, a plurality of subpixels included in a pixel may be connectedto the same gate line.

At least part of this embodiment can be implemented in combination withany of the embodiments described in this specification as appropriate.

Embodiment 2

In this embodiment, a touch panel of one embodiment of the presentinvention will be described.

Structure Example

FIGS. 19A and 19B are perspective views of a touch panel 505. FIG. 19B aschematic perspective developed view of FIG. 19A. Note that only maincomponents are illustrated for simplicity.

The touch panel 505 includes the display device 10 and a substrate 590having a touch sensor 595.

Embodiment 1 can be referred to for the structure of the display device10. The display device 10 here includes an FPC 509(1), a terminalportion 519, a wiring 511, and a circuit 503 s, for example.

The substrate 590 includes the touch sensor 595 and a plurality ofwirings 598 electrically connected to the touch sensor 595. Theplurality of wirings 598 are led to a peripheral portion of thesubstrate 590, and part of the plurality of wirings 598 form a terminal.The terminal is electrically connected to an FPC 509(2). Note that inFIG. 19B, electrodes, wirings, and the like of the touch sensor 595provided on the back side of the substrate 590 (on the substrate 101side) are indicated by solid lines for clarity.

As the touch sensor 595, a capacitive touch sensor can be used. Examplesof the capacitive touch sensor are a surface capacitive touch sensor anda projected capacitive touch sensor.

Examples of the projected capacitive touch sensor are a self-capacitivetouch sensor and a mutual capacitive touch sensor, which differ mainlyin the driving method. The use of a mutual capacitive touch sensor ispreferable because multiple points can be sensed simultaneously.

An example of using a projected capacitive touch sensor will bedescribed below.

Note that a variety of sensors that can sense the closeness or thecontact of a sensing target such as a finger can be used.

The projected capacitive touch sensor 595 includes electrodes 591 andelectrodes 592. The electrodes 591 are electrically connected to any ofthe plurality of wirings 598, and the electrodes 592 are electricallyconnected to any of the other wirings 598.

The electrodes 592 each have a shape of a plurality of quadranglesarranged in one direction with one corner of a quadrangle connected toone corner of another quadrangle as illustrated in FIGS. 19A and 19B.

The electrodes 591 each have a quadrangular shape and are arranged in adirection intersecting with the direction in which the electrodes 592extend.

A wiring 594 electrically connects two electrodes 591 between which oneelectrode 592 is positioned. The intersecting area of the electrode 592and the wiring 594 is preferably as small as possible. Such a structureenables a reduction in the area of a region where the electrodes are notprovided, reducing unevenness in transmittance. As a result, unevennessin luminance of light from the touch sensor 595 can be reduced.

Note that the shapes of the electrodes 591 and the electrodes 592 arenot limited to the above-mentioned shapes and can be any of a variety ofshapes. For example, a plurality of electrodes 591 may be arranged sothat the space between two adjacent electrodes are reduced as much aspossible, and a plurality of electrodes 592 may be arranged so as tointersect with the electrodes 591 with an insulating layer providedbetween the adjacent electrodes 592. In that case, two adjacentelectrodes may be spaced apart from each other. Moreover, between thetwo adjacent electrodes 592, a dummy electrode which is electricallyinsulated from these electrodes is preferably provided, whereby the areaof a region having a different transmittance can be reduced.

The touch sensor 595 includes the substrate 590, the electrodes 591 andthe electrodes 592 provided in a staggered arrangement on the substrate590, an insulating layer covering the electrodes 591 and the electrodes592, and the wiring 594 that electrically connects the adjacentelectrodes 591 to each other.

An adhesive layer 597 bonds the substrate 590 to the substrate 570 sothat the touch sensor 595 overlaps with the display portion 501.

The electrodes 591 and the electrodes 592 are formed using alight-transmitting conductive material. As the light-transmittingconductive material, a conductive oxide such as indium oxide, indium tinoxide, indium zinc oxide, zinc oxide, or zinc oxide to which gallium isadded can be used. Note that a film including graphene may be used aswell. The film containing graphene can be formed, for example, byreducing a film containing graphene oxide. As a reducing method, amethod with application of heat or the like can be employed.

The electrodes 591 and 592 may have a mesh shape such that mesh openingsand light-emitting elements overlap with each other. In this case, alow-conductive metal or alloy, for example, can be used for theelectrodes 591 and 592.

Note that, for example, a low-resistance material is preferably used asa material of conductive films such as the electrode 591 and theelectrode 592, i.e., a wiring and an electrode in the touch panel. Forexample, silver, copper, aluminum, a carbon nanotube, graphene, a metalhalide (e.g., a silver halide), or the like may be used. Alternatively,a metal nanowire including a number of conductors with an extremelysmall width (for example, a diameter of several nanometers) may be used.Further alternatively, a net-like metal mesh with a conductor may beused. For example, an Ag nanowire, a Cu nanowire, an Al nanowire, an Agmesh, a Cu mesh, or an Al mesh may be used. In the case of using an Agnanowire, light transmittance of 89% or more and a sheet resistance of40 ohm/square or more and 100 ohm/square or less can be achieved. Notethat because of having high transmittance, a metal nanowire, a metalmesh, a carbon nanotube, graphene, or the like may be used as anelectrode of the display element, such as a pixel electrode or a commonelectrode.

One of the electrodes 592 extends in one direction, and a plurality ofelectrodes 592 are provided in the form of stripes.

The wiring 594 intersects with the electrodes 592.

Adjacent electrodes 591 are provided with one of the electrodes 592provided therebetween. The wiring 594 electrically connects the adjacentelectrodes 591.

Note that the plurality of electrodes 591 is not necessarily arranged inthe direction orthogonal to one electrode 592 and may be arranged tointersect with one electrode 592 at an angle of less than 90°.

One wiring 598 is electrically connected to any of the electrodes 591and the electrodes 592. Part of the wiring 598 serves as a terminal. Forthe wiring 598, a metal material such as aluminum, gold, platinum,silver, nickel, titanium, tungsten, chromium, molybdenum, iron, cobalt,copper, or palladium or an alloy material containing any of these metalmaterials can be used.

In addition, the connection layer 599 electrically connects the wiring598 with the FPC 509(2). For the connection layer 599, various kinds ofanisotropic conductive film or paste or the like can be used.

Although the substrate 590 having the touch sensor 595 overlaps with thedisplay device 10 in this non-limiting example, the touch sensor 595 maybe formed on a surface of the second substrate 102 opposite to the firstsubstrate 101. The touch sensor 595 may be provided between the firstsubstrate 101 and the second substrate 102, in which case the touchsensor 595 is preferably provided between a coloring layer and thesecond substrate 102, for example.

The use of flexible materials for the first substrate 101, the secondsubstrate 102, and the substrate 590 can form a flexible touch panel inwhich the pixel portion can be bent.

At least part of this embodiment can be implemented in combination withany of the embodiments described in this specification as appropriate.

Embodiment 3

In this embodiment, an example of a method for operating the touch panelof one embodiment of the present invention is described with referenceto drawings.

Example of Sensing Method of Sensor

FIG. 20A is a block diagram illustrating the structure of a mutualcapacitive touch sensor. FIG. 20A illustrates a pulse voltage outputcircuit 601 and a current sensing circuit 602. Note that in FIG. 20A,six wirings X1 to X6 represent the electrodes 621 to which a pulsevoltage is applied, and six wirings Y1 to Y6 represent the electrodes622 that detect changes in current. FIG. 20A also illustrates acapacitor 603 that is formed between the electrodes 621 and 622. Notethat functional replacement between the electrodes 621 and 622 ispossible.

The pulse voltage output circuit 601 is a circuit for sequentiallyapplying a pulse voltage to the wirings X1 to X6. By application of apulse voltage to the wirings X1 to X6, an electric field is generatedbetween the electrodes 621 and 622 of the capacitor 603. When theelectric field between the electrodes is shielded, for example, a changeoccurs in the capacitor 603 (mutual capacitance). The approach orcontact of a sensing target can be sensed by utilizing this change.

The current sensing circuit 602 is a circuit for detecting changes incurrent flowing through the wirings Y1 to Y6 that are caused by thechange in mutual capacitance in the capacitor 603. No change in currentvalue is detected in the wirings Y1 to Y6 when there is no approach orcontact of a sensing target, whereas a decrease in current value isdetected when mutual capacitance is decreased owing to the approach orcontact of a sensing target. Note that an integrator circuit or the likeis used for sensing of current values.

FIG. 20B is a timing chart showing input and output waveform is in themutual capacitive touch sensor illustrated in FIG. 20A. In FIG. 20B,sensing of a sensing target is performed in all the rows and columns inone frame period. FIG. 20B shows a period when a sensing target is notsensed (not touched) and a period when a sensing target is sensed(touched). Sensed current values of the wirings Y1 to Y6 are shown asthe waveforms of voltage values.

A pulse voltage is sequentially applied to the wirings X1 to X6, and thewaveforms of the wirings Y1 to Y6 change in accordance with the pulsevoltage. When there is no approach or contact of a sensing target, thewaveforms of the wirings Y1 to Y6 change in accordance with changes inthe voltages of the wirings X1 to X6. The current value is decreased atthe point of approach or contact of a sensing target and accordingly thewaveform of the voltage value changes.

By detecting a change in mutual capacitance in this manner, the approachor contact of a sensing target can be sensed.

Although FIG. 20A is a passive type touch sensor in which only thecapacitor 603 is provided at the intersection of wirings as a touchsensor, an active type touch sensor including a transistor and acapacitor may be used. FIG. 21 is a sensor circuit included in an activematrix type touch sensor.

The sensor circuit includes the capacitor 603 and transistors 611, 612,and 613. A signal G2 is input to a gate of the transistor 613. A voltageVRES is applied to one of a source and a drain of the transistor 613,and one electrode of the capacitor 603 and a gate of the transistor 611are electrically connected to the other of the source and the drain ofthe transistor 613. One of a source and a drain of the transistor 611 iselectrically connected to one of a source and a drain of the transistor612, and a voltage VSS is applied to the other of the source and thedrain of the transistor 611. A signal G1 is input to a gate of thetransistor 612, and a wiring ML is electrically connected to the otherof the source and the drain of the transistor 612. The voltage VSS isapplied to the other electrode of the capacitor 603.

Next, the operation of the sensor circuit will be described. First, apotential for turning on the transistor 613 is supplied as the signalG2, and a potential with respect to the voltage VRES is thus applied tothe node n connected to the gate of the transistor 611. Then, apotential for turning off the transistor 613 is applied as the signalG2, whereby the potential of the node n is maintained.

Then, mutual capacitance of the capacitor 603 changes owing to theapproach or contact of a sensing target such as a finger, andaccordingly the potential of the node n is changed from VRES.

In reading operation, a potential for turning on the transistor 612 issupplied as the signal G1. A current flowing through the transistor 611,that is, a current flowing through the wiring ML is changed inaccordance with the potential of the node n. By sensing this current,the approach or contact of a sensing target can be sensed.

It is preferred that the transistors 611, 612, and 613 each include anoxide semiconductor in a semiconductor layer where a channel is formed.In particular, by using an oxide semiconductor in a semiconductor layerwhere a channel of the transistor 613 is formed, the potential of thenode n can be held for a long time and the frequency of operation(refresh operation) of resupplying VRES to the node n can be reduced.

At least part of this embodiment can be implemented in combination withany of the embodiments described in this specification as appropriate.

Embodiment 4

In this embodiment, electronic devices and lighting devices of oneembodiment of the present invention will be described with reference todrawings.

Highly reliable electronic devices and highly reliable lighting devicescan be fabricated using the display device of one embodiment of thepresent invention. Highly reliable electronic devices and highlyreliable lighting devices having a curved surface can be fabricatedusing the display device of one embodiment of the present invention.Highly reliable electronic devices and highly reliable lighting deviceshaving flexibility can be fabricated using the display device of oneembodiment of the present invention.

Examples of electronic devices include a television set (also referredto as a television or a television receiver), a monitor of a computer orthe like, a digital camera, a digital video camera, a digital photoframe, a mobile phone (also referred to as a mobile phone device), aportable game machine, a portable information terminal, an audioreproducing device, a large-sized game machine such as a pinballmachine, and the like.

The electronic device or the lighting device of one embodiment of thepresent invention has flexibility and therefore can be incorporatedalong a curved inside-outside wall surface of a house or a building or acurved interior/exterior surface of a car.

Furthermore, the electronic device of one embodiment of the presentinvention may include a secondary battery. It is preferable that thesecondary battery be capable of being charged by non-contact powertransmission.

Examples of the secondary battery include a lithium ion secondarybattery such as a lithium polymer battery using a gel electrolyte(lithium ion polymer battery), a nickel-hydride battery, anickel-cadmium battery, an organic radical battery, a lead-acid battery,an air secondary battery, a nickel-zinc battery, and a silver-zincbattery.

The electronic device of one embodiment of the present invention mayinclude an antenna. When a signal is received by the antenna, theelectronic device can display an image, data, or the like on a displayportion. When the electronic device includes a secondary battery, theantenna may be used for contactless power transmission.

FIGS. 22A, 22B, 22C1, 22C2, 22D, and 22E illustrate an example of anelectronic device including a display portion 7000 with a curvedsurface. The display surface of the display portion 7000 is bent, andimages can be displayed on the bent display surface. The display portion7000 may be flexible.

The display portion 7000 can be formed using the display device or thelike of one embodiment of the present invention. One embodiment of thepresent invention makes it possible to provide a highly reliableelectronic device having a curved display portion.

FIG. 22A illustrates an example of a mobile phone. A mobile phone 7100includes a housing 7101, the display portion 7000, operation buttons7103, an external connection port 7104, a speaker 7105, a microphone7106, and the like.

The mobile phone 7100 illustrated in FIG. 22A includes a touch sensor inthe display portion 7000. Moreover, operations such as making a call andinputting a letter can be performed by touch on the display portion 7000with a finger, a stylus, or the like.

With the operation buttons 7103, power ON or OFF can be switched. Inaddition, types of images displayed on the display portion 7000 can beswitched; switching images from a mail creation screen to a main menuscreen, for example.

FIG. 22B illustrates an example of a television set. In the televisiondevice 7200, the display portion 7000 is incorporated into the housing7201. Here, the housing 7201 is supported by a stand 7203.

The television set 7200 illustrated in FIG. 22B can be operated with anoperation switch of the housing 7201 or a separate remote controller7211. The display portion 7000 may include a touch sensor. The displayportion 7000 can be operated by touching the display portion with afinger or the like. The remote controller 7211 may be provided with adisplay portion for displaying data output from the remote controller7211. With operation buttons or a touch panel of the remote controller7211, channels and volume can be controlled and images displayed on thedisplay portion 7000 can be controlled.

The television set 7200 is provided with a receiver, a modem, and thelike. A general television broadcast can be received with the receiver.When the television set is connected to a communication network with orwithout wires via the modem, one-way (from a transmitter to a receiver)or two-way (between a transmitter and a receiver or between receivers)data communication can be performed.

FIGS. 22C1, 22C2, 22D, and 22E illustrate an example of a portableinformation terminal. Each of the portable information terminalsincludes a housing 7301 and the display portion 7000. Each of theportable information terminals may also include an operation button, anexternal connection port, a speaker, a microphone, an antenna, abattery, or the like. The display portion 7000 is provided with a touchsensor. An operation of the portable information terminal can beperformed by touching the display portion 7000 with a finger, a stylus,or the like.

FIG. 22C1 is a perspective view of a portable information terminal 7300.FIG. 22C2 is a top view of the portable information terminal 7300. FIG.22D is a perspective view of a portable information terminal 7310. FIG.22E is a perspective view of a portable information terminal 7320.

Each of the portable information terminals functions as, for example,one or more of a telephone set, a notebook, and an information browsingsystem. Specifically, each of the portable information terminals can beused as a smartphone. Each of the portable information terminals iscapable of executing a variety of applications such as mobile phonecalls, e-mailing, reading and editing texts, music reproduction,Internet communication, and a computer game, for example.

The portable information terminals 7300, 7310, and 7320 can displaycharacters and image information on its plurality of surfaces. Forexample, as illustrated in FIGS. 22C1 and 22D, three operation buttons7302 can be displayed on one surface, and information 7303 indicated bya rectangle can be displayed on another surface. FIG. 22C2 illustratesan example in which information 7303 is displayed at the top of theportable information terminal. FIG. 22D illustrates an example in whichinformation 7303 is displayed on the side of the portable informationterminal. Information may be displayed on three or more surfaces of theportable information terminal. FIG. 22E illustrates an example whereinformation 7304, information 7305, and information 7306 are displayedon different surfaces.

Examples of the information include notification from a socialnetworking service (SNS), display indicating reception of an e-mail oran incoming call, the title of an e-mail, the sender of an e-mail, thedate, the time, remaining battery, the reception strength of an antenna,and the like. Alternatively, the operation button, an icon, or the likemay be displayed instead of the information.

For example, a user of the portable information terminal 7300 can seethe display (here, the information 7303) with the portable informationterminal 7300 put in a breast pocket of his/her clothes.

Specifically, a caller's phone number, name, or the like of an incomingcall is displayed in a position that can be seen from above the portableinformation terminal 7300. Thus, the user can see the display withouttaking out the portable information terminal 7300 from the pocket anddecide whether to answer the call.

FIGS. 22F to 22H each illustrate an example of a lighting device havinga curved light-emitting portion.

The light-emitting portion included in each of the lighting devicesillustrated in FIGS. 22F to 22H can be manufactured using the displaydevice or the like of one embodiment of the present invention. Oneembodiment of the present invention makes it possible to provide ahighly reliable lighting device having a curved light-emitting portion.

A lighting device 7400 illustrated in FIG. 22F includes a light-emittingportion 7402 with a wave-shaped light-emitting surface and thus is agood-design lighting device.

A light-emitting portion 7412 included in the lighting device 7410illustrated in FIG. 22G has two convex-curved light-emitting portionssymmetrically placed. Thus, all directions can be illuminated with thelighting device 7410 as a center.

A lighting device 7420 illustrated in FIG. 22H includes a concave-curvedlight-emitting portion 7422. This is suitable for illuminating aspecific range because light emitted from the concave-curvedlight-emitting portion 7422 is collected to the front of the lightingdevice 7420. In addition, with this structure, a shadow is less likelyto be produced.

The light-emitting portion included in each of the lighting devices7400, 7410 and 7420 may be flexible. The light-emitting portion may befixed on a plastic member, a movable frame, or the like so that anemission surface of the light-emitting portion can be bent freelydepending on the intended use.

The lighting devices 7400, 7410, and 7420 each include a stage 7401provided with an operation switch 7403 and a light-emitting portionsupported by the stage 7401.

Note that although the lighting device in which the light-emittingportion is supported by the stage is described as an example here, ahousing provided with a light-emitting portion can be fixed on a ceilingor suspended from a ceiling. Since the light-emitting surface can becurved, the light-emitting surface can be deformed to have a depressedshape, whereby a particular region can be brightly illuminated, or thelight-emitting surface is deformed to have a projecting shape, whereby awhole room can be brightly illuminated.

FIGS. 23A1, 23A2, 23B, 23C, 23D, 23E, 23F, 23G, 23H, and 23I eachillustrate an example of a portable information terminal including adisplay portion 7001 having flexibility.

The display portion 7001 included in each of the portable informationterminals is manufactured using the light-emitting device, the displaydevice, the input-output device, or the like of one embodiment of thepresent invention. For example, a light-emitting device, a displaydevice, or an input-output device that can be bent with a radius ofcurvature of greater than or equal to 0.01 mm and less than or equal to150 mm can be used. The display portion 7001 may include a touch sensorso that the portable information terminal can be operated by touchingthe display portion 7001 with a finger or the like. One embodiment ofthe present invention makes it possible to provide an electronic deviceincluding a display portion having flexibility with a high yield.

FIGS. 23A1 and 23A2 are a perspective views and a side view illustratingan example of the portable information terminal. A portable informationterminal 7500 includes a housing 7501, the display portion 7001, adisplay portion tab 7502, operation buttons 7503, or the like.

The portable information terminal 7500 includes a rolled flexibledisplay portion 7001 in the housing 7501.

The portable information terminal 7500 can receive a video signal with acontrol portion incorporated therein and can display the received videoon the display portion 7001. The portable information terminal 7500incorporates a battery. A terminal portion for connecting a connectormay be included in the housing 7501 so that a video signal or power canbe directly supplied from the outside with a wiring.

By pressing the operation buttons 7503, power ON/OFF, switching ofdisplayed videos, and the like can be performed. Although FIGS. 23A1,23A2, and 23B illustrate an example where the operation buttons 7503 arepositioned on a side surface of the portable information terminal 7500,one embodiment of the present invention is not limited thereto. Theoperation buttons 7503 may be placed on a display surface (a frontsurface) or a rear surface of the portable information terminal 7500.

FIG. 23B illustrates the portable information terminal 7500 in a statewhere the display portion 7001 is pulled out with the display portiontab 7502. Videos can be displayed on the display portion 7001 in thisstate. In addition, the portable information terminal 7500 may performdifferent displays in the state where part of the display portion 7001is rolled as shown in FIG. 23A1 and in the state where the displayportion 7001 is pulled out as shown in FIG. 23B. For example, in thestate shown in FIG. 23A1, the rolled portion of the display portion 7001is put in a non-display state, which results in a reduction in powerconsumption of the portable information terminal 7500.

A reinforcement frame may be provided for a side portion of the displayportion 7001 so that the display portion 7001 has a flat display surfacewhen pulled out.

Note that in addition to this structure, a speaker may be provided forthe housing so that sound is output with an audio signal receivedtogether with a video signal.

FIGS. 23C to 23E illustrate an example of a foldable portableinformation terminal. FIG. 23C illustrates a portable informationterminal 7600 that is opened. FIG. 23D illustrates the portableinformation terminal 7600 that is being opened or being folded. FIG. 23Eillustrates the portable information terminal 7600 that is folded. Theportable information terminal 7600 is highly portable when folded, andis highly browsable when opened because of a seamless large displayarea.

A display portion 7001 is supported by three housings 7601 joinedtogether by hinges 7602. By folding the portable information terminal7600 at a connection portion between two housings 7601 with the hinges7602, the portable information terminal 7600 can be reversibly changedin shape from an opened state to a folded state.

FIGS. 23F and 23G illustrate an example of a foldable portableinformation terminal. FIG. 23F illustrates a portable informationterminal 7650 that is folded so that the display portion 7001 is on theinside. FIG. 23G illustrates the portable information terminal 7650 thatis folded so that the display portion 7001 is on the outside. Theportable information terminal 7650 includes the display portion 7001 anda non-display portion 7651. When the portable information terminal 7650is not used, the portable information terminal 7650 is folded so thatthe display portion 7001 is on the inside, whereby the display portion7001 can be prevented from being contaminated or damaged.

FIG. 23H illustrates an example of a flexible portable informationterminal. A portable information terminal 7700 includes a housing 7701and the display portion 7001. The portable information terminal 7700 mayinclude buttons 7703 a and 7703 b which serve as input means, speakers7704 a and 7704 b which serve as sound output means, an externalconnection port 7705, a microphone 7706, or the like. A flexible battery7709 can be mounted on the portable information terminal 7700. Thebattery 7709 may be arranged to overlap with the display portion 7001,for example.

The housing 7701, the display portion 7001, the battery 7709 areflexible. Thus, it is easy to curve the portable information terminal7700 into a desired shape or to twist the portable information terminal7700. For example, the portable information terminal 7700 can be curvedso that the display portion 7001 is on the inside or in the outside. Theportable information terminal 7700 can be used in a rolled state. Sincethe housing 7701 and the display portion 7001 can be transformed freelyin this manner, the portable information terminal 7700 is less likely tobe broken even when the portable information terminal 7700 falls down orexternal stress is applied to the portable information terminal 7700.

The portable information terminal 7700 can be used effectively invarious situations because the portable information terminal 7700 islightweight. For example, the portable information terminal 7700 can beused in the state where the upper portion of the housing 7701 issuspended by a clip or the like, or in the state where the housing 7701is fixed to a wall by magnets or the like.

FIG. 23I illustrates an example of a wrist-watch-type portableinformation terminal. The portable information terminal 7800 includes aband 7801, the display portion 7001, an input-output terminal 7802,operation buttons 7803, or the like. The band 7801 has a function of ahousing. A flexible battery 7805 can be mounted on the portableinformation terminal 7800. The battery 7805 may overlap with the displayportion 7001 and the band 7801, for example.

The band 7801, the display portion 7001, and the battery 7805 haveflexibility. Thus, the portable information terminal 7800 can be easilycurved to have a desired shape.

With the operation buttons 7803, a variety of functions such as timesetting, ON/OFF of the power, ON/OFF of wireless communication, settingand cancellation of silent mode, and setting and cancellation of powersaving mode can be performed. For example, the functions of theoperation button 7803 can be set freely by the operating systemincorporated in the portable information terminal 7800.

By touching an icon 7804 displayed on the display portion 7001 with afinger or the like, application can be started.

The portable information terminal 7800 can employ near fieldcommunication that is a communication method based on an existingcommunication standard. In that case, for example, mutual communicationbetween the portable information terminal 7800 and a headset capable ofwireless communication can be performed, and thus hands-free calling ispossible.

In the case where the input-output terminal 7802 is included in theportable information terminal 7800, data can be directly transmitted toand received from another information terminal via a connector. Chargingthrough the input-output terminal 7802 is also possible. Note thatcharging of the portable information terminal described as an example inthis embodiment can be performed by non-contact power transmissionwithout using the input-output terminal.

FIG. 24A is an external view of an automobile 9700. FIG. 24B illustratesa driver's seat of the automobile 9700. The automobile 9700 includes acar body 9701, wheels 9702, a dashboard 9703, lights 9704, and the like.The display device of one embodiment of the present invention can beused in a display portion or the like of the automobile 9700. Forexample, the display device of one embodiment of the present inventioncan be used in display portions 9710 to 9715 illustrated in FIG. 24B.

The display portion 9710 and the display portion 9711 are displaydevices provided in an automobile windshield. The display device of oneembodiment of the present invention can be a see-through display device,through which the opposite side can be seen, by using alight-transmitting conductive material for its electrodes. Such asee-through display device does not hinder driver's vision duringdriving the automobile 9700. Therefore, the display device of oneembodiment of the present invention can be provided in the windshield ofthe automobile 9700. Note that in the case where a transistor or thelike for driving the display device is provided in the display device, atransistor having light-transmitting properties, such as an organictransistor using an organic semiconductor material or a transistor usingan oxide semiconductor, is preferably used.

The display portion 9712 is a display device provided on a pillarportion. For example, an image taken by an imaging unit provided in thecar body is displayed on the display portion 9712, whereby the viewhindered by the pillar portion can be compensated. The display portion9713 is a display device provided on the dashboard. For example, animage taken by an imaging unit provided in the car body is displayed onthe display portion 9713, whereby the view hindered by the dashboard canbe compensated. That is, by displaying an image taken by an imaging unitprovided on the outside of the automobile, blind areas can be eliminatedand safety can be increased. Displaying an image to compensate for thearea which a driver cannot see, makes it possible for the driver toconfirm safety easily and comfortably.

FIG. 24C illustrates the inside of a car in which bench seats are usedfor a driver seat and a front passenger seat. A display portion 9721 isa display device provided in a door portion. For example, an image takenby an imaging unit provided in the car body is displayed on the displayportion 9721, whereby the view hindered by the door can be compensated.A display portion 9722 is a display device provided in a steering wheel.A display portion 9723 is a display device provided in the middle of aseating face of the bench seat. Note that the display device can be usedas a seat heater by providing the display device on the seating face orbackrest and by using heat generation of the display device as a heatsource.

The display portion 9714, the display portion 9715, and the displayportion 9722 can display a variety of kinds of information such asnavigation data, a speedometer, a tachometer, a mileage, a fuel meter, agearshift indicator, and air-condition setting. The content, layout, orthe like of the display on the display portions can be changed freely bya user as appropriate. The information listed above can also bedisplayed on the display portions 9710 to 9713, 9721, and 9723. Thedisplay portions 9710 to 9715 and 9721 to 9723 can also be used aslighting devices. The display portions 9710 to 9715 and 9721 to 9723 canalso be used as heating devices.

The display portion including the display device of one embodiment ofthe present invention can be flat, in which case the display device doesnot necessarily have a curved surface or flexibility.

FIG. 24D illustrates a portable game console including a housing 901, ahousing 902, a display portion 903, a display portion 904, a microphone905, a speaker 906, an operation button 907, a stylus 908, and the like.

The portable gate console shown in FIG. 24D includes two displayportions 903 and 904. Note that the number of display portions of anelectronic device of one embodiment of the present invention is notlimited to two and can be one or three or more as long as at least onedisplay portion includes the display device of one embodiment of thepresent invention.

FIG. 24E illustrates a laptop personal computer, which includes ahousing 921, a display portion 922, a keyboard 923, a pointing device924, and the like.

The display device of one embodiment of the present invention can beused in the display portion 922.

FIG. 25A is an external view of a camera 8000. The camera 8000 includesa housing 8001, a display portion 8002, an operation button 8003, ashutter button 8004, and a connection portion 8005. A lens 8006 can beput on the camera 8000.

The connection portion 8005 includes an electrode to connect with afinder 8100, which is described below, a stroboscope, or the like.

Although the lens 8006 of the camera 8000 here is detachable from thehousing 8001 for replacement, the lens 8006 may be included in a housing8001.

Images can be taken at the touch of the shutter button 8004. Inaddition, images can be taken at the touch of the display portion 8002which serves as a touch panel.

The display device of one embodiment of the present invention can beused in the display portion 8002.

FIG. 25B shows the camera 8000 with the finder 8100 connected.

The finder 8100 includes a housing 8101, a display portion 8102, and abutton 8103.

The housing 8101 includes a connection portion for the camera 8000 andthe connection portion 8005, and the finder 8100 can be connected to thecamera 8000. The connection portion includes an electrode, and an imageor the like received from the camera 8000 through the electrode can bedisplayed on the display portion 8102.

The button 8103 has a function of a power button, and the displayportion 8102 can be turned on and off by the button 8103.

The display device of one embodiment of the present invention can beused in the display portion 8102.

Although the camera 8000 and the finder 8100 are separate and detachableelectronic devices in FIGS. 25A and 25B, the housing 8001 of the camera8000 may include a finder having a display device of one embodiment ofthe present invention.

FIG. 25C illustrates an external view of a head-mounted display 8200.

The head-mounted display 8200 includes a mounting portion 8201, a lens8202, a main body 8203, a display portion 8204, a cable 8205. Themounting portion 8201 includes a battery 8206.

Power is supplied from the battery 8206 to the main body 8203 throughthe cable 8205. The main body 8203 includes a wireless receiver or thelike to receive video data, such as image data, and display it on thedisplay portion 8204. The movement of the eyeball and the eyelid of auser is captured by a camera in the main body 8203 and then coordinatesof the points the user looks at are calculated based on the captureddata to utilize the eye point of the user as an input means.

The mounting portion 8201 may include a plurality of electrodes incontact with the user. The main body 8203 may be configured to sensecurrent flowing through the electrodes with the movement of the user'seyeball to recognize the location of his eye. The main body 8203 may beconfigured to sense current flowing through the electrodes to monitorthe user's pulse. The mounting portion 8201 may include sensors, such asa temperature sensor, a pressure sensor, or an acceleration sensor anddisplay the user's biological information on the display portion 8204.The main body 8203 may be configured to sense the movement of the user'shead to move an image displayed on the display portion 8204 insynchronization with the movement of the user's head.

The display device of one embodiment of the present invention can beused in the display portion 8204.

At least part of this embodiment can be implemented in combination withany of the embodiments described in this specification as appropriate.

Example 1

A display panel (a display device) of one embodiment of the presentinvention was fabricated in this example.

One glass substrate over which a transistor and a light-emitting elementwere formed and another glass substrate over which a coloring layer wasformed were bonded together to fabricate the display panel in thisexample.

As the transistor, a transistor including a c-axis aligned crystallineoxide semiconductor (CAAC-OS) was used. Since the CAAC-OS, which is notamorphous, has few defect states, using the CAAC-OS can improve thereliability of the transistor. Moreover, since the CAAC-OS does not havea grain boundary, a stable and uniform film can be formed over a largearea and stress that is caused by bending a flexible light-emittingdevice does not easily make a crack in a CAAC-OS film.

A CAAC-OS is a crystalline oxide semiconductor having c-axis alignmentof crystals in a direction substantially perpendicular to the filmsurface. It has been found that oxide semiconductors have a variety ofcrystal structures other than a single-crystal structure. An example ofsuch structures is a nano-crystal (nc) structure, which is an aggregateof nanoscale microcrystals. The crystallinity of a CAAC-OS structure islower than that of a single-crystal structure and higher than that of annc structure.

In this example, a channel-etched transistor including an In—Ga—Zn-basedoxide was used. The transistor was fabricated over a glass substrate ata process temperature lower than 500° C.

In a method of fabricating an element such as a transistor directly overan organic resin such as a plastic substrate, the temperature of theprocess for fabricating the element needs to be lower than the uppertemperature limit of the organic resin. In this example, the formationsubstrate is a glass substrate and the peeling layer, which is aninorganic film, has high heat resistance; thus, the transistor can befabricated at a temperature equal to that when a transistor isfabricated over a glass substrate. Thus, the performance and reliabilityof the transistor can be easily secured.

FIG. 26 shows Id-Vg characteristics of the transistors fabricated inthis example. The transistor has a channel width of approximately 2 μmand a channel length of approximately 3.25 μm, to which 1.5-μm designrule is applied. Measurement was performed under two conditions at thesource-drain voltages of 0.1 V and 10 V. As shown in FIG. 26, thetransistor fabricated in this example shows normally-off characteristicsand high uniformity despite its small channel length and width. Inaddition, the value of drain current is extremely small when the gatevoltage is lower than or equal to 0 V.

As the light-emitting element, a tandem (stacked-layer) organic ELelement emitting white light was used. The light-emitting element has atop emission structure, where light generated by the light-emittingelement is extracted to the outside of the light-emitting panel througha color filter. The pixel configuration shown in FIG. 5A is used. Thepixel layout shown in FIGS. 14A and 14B is used.

The size of a display portion of the fabricated display panel is 2.78inches in diagonal, the number of pixels is 2560×1440, the resolution(pixel density) is 1058 ppi, the pixel size is 24 μm×24 μm (8 μm×RGB×24μm), and the aperture ratio is 30.4%. The display panel has a framefrequency of 60 Hz, a built-in scan driver, and a COF-mounted sourcedriver.

FIG. 27A is a photograph of the 1058-ppi display panel, which is anextremely high-resolution display using thin film transistors over aglass substrate.

FIG. 27B is a photograph of the display panel taken through a lens.Since the resolution of the display panel is extremely high, the pixelsare not visually distinguishable even when the image is enlarged, and afine image can thus be displayed. The display panel can be used for aview finder, for example.

The above description thus far is Example 1.

Example 2

The color reproducibility of the display panel was examined in thisexample.

In a light-emitting element with a tandem structure in which two or morelight-emitting units are stacked, an intermediate layer having highconductivity between two of the light-emitting units can reduce drivingvoltage. The increase in pixel resolution, however, leads to flow-in ofcurrent between adjacent pixels via the intermediate layer so that theadjacent pixel which should not emit emits light, which causes a problemof reduction in color reproducibility. Such a phenomenon can be referredto as crosstalk.

FIG. 28 is a schematic view of a stacked-layer structure of thelight-emitting element having a tandem structure in which twolight-emitting units are stacked. The light-emitting element includes alight-emitting unit including a light-emitting layer containing a bluefluorescent material, and a light-emitting unit including alight-emitting layer containing a green phosphorescent material and alight-emitting layer containing a red phosphorescent material. Thelight-emitting element includes an intermediate layer between thelight-emitting layer containing a blue fluorescent material and thelight-emitting layer containing a green phosphorescent material.

The intermediate layer of the light-emitting element used in thisexample has a stacked structure of a layer containing lithium oxide withhigh conductivity and a layer containing an electron transport material(also referred to as an electron transport layer). The electrontransport layer is between the layer containing lithium oxide and ananode.

Two measures to reduce the influence of crosstalk were taken in thisexample.

The first measure is to provide a gap spacer (corresponding to thespacer 215 in FIG. 16) between adjacent pixels. An expected effect isthat the thickness of the intermediate layer is reduced and theresistance is accordingly increased on the side surfaces of the gapspacer, so that current flow-in between adjacent pixels via theintermediate layer can be suppressed.

The second measure is to change the structure of the intermediate layer.Although there was an idea for suppressing the influence of crosstalkthat the thickness of a layer containing lithium oxide with highconductivity was reduced in order to reduce the conductivity of anintermediate layer, it was difficult to further reduce the thickness ofthe layer containing lithium oxide with high conductivity and fabricatea light-emitting element in terms of thickness control because of itsextremely small thickness (approximately 0.1 nm). In addition, a furtherreduction in thickness of the layer containing lithium oxide might causean increase in driving voltage of a light-emitting element. As a resultof examination, lithium, which was contained in the layer containinglithium oxide, has been found to be likely to diffuse into an electrontransport layer. Thus, a measure to reduce not the thickness of thelayer containing lithium oxide with high conductivity but the thicknessof the electron transport layer which was in contact with the layer fromapproximately 15 nm to 10 nm was taken.

In this example, three kinds of samples (display panels) were fabricatedby a method similar to that in Example 1: a reference sample 1 (“Ref 1”)is a display panel without a gap spacer; a sample 1 (“Sample 1”) is adisplay panel with a gap spacer; and a sample 2 (“Sample 2”) is adisplay panel without a gap spacer in which the structure of theintermediate layer of the light-emitting element is optimized.

FIGS. 29A and 29B are a chromaticity diagram for the reference sample 1and the sample 1 and that of the sample 2, respectively.

As seen from FIG. 29A, the color reproducibility of the sample 1, whichhas a gap spacer, is higher than that of the reference sample 1, whichdoes not have. Similarly, the color reproducibility of the sample 2, inwhich the structure of the intermediate layer was changed, is alsoimproved as seen from FIG. 29B.

FIG. 30 shows luminance dependence of NTSC ratio of each sample. Theresults of FIG. 30 show that the influence of crosstalk becomes morepronounced on the lower-luminance side than on the higher-luminanceside. In addition, the amount of change of NTSC ratio with respect tothe luminance is smaller in the samples 1 and 2 than in the referencesample 1, which means the samples 1 and 2 have high colorreproducibility.

Thus, a gap spacer can suppress the influence of crosstalk. In the caseof fabricating a display panel in which a gap between substrates isreduced to lower the viewing angle dependency, it is effective to changea structure of an intermediate layer without providing a gap spacer, asin the sample 2. The NTSC ratio of the sample 2, which has no gapspacer, is high, approximately 88% when the luminance was 100 cd/m² orhigher.

The above description thus far is Example 2.

Example 3

In this example, a display panel of one embodiment of the presentinvention was fabricated and the color reproducibility and the viewingangle dependency were examined.

In this example, three kinds of samples (display panels) were fabricatedby a method similar to that in Example 1: a reference sample 2 (“Ref.2”) is a display panel without a gap spacer; a sample 3 (“Sample 3”) isa display panel with a gap spacer; and a sample 4 (“Sample 4”) is adisplay panel without a gap spacer in which a measure to reduce theconductivity of an electron transport layer of a light-emitting elementhas been taken.

In addition, a reference sample 3 (“Ref. 3”) with a lower resolutionthan those of the sample 3, the sample 4, and the reference sample 2 wasfabricated. The size of a display portion of the display panel which wasused as the reference sample 3 was 9.2 inches in diagonal, the number ofpixels was 1080×1920, the resolution (pixel density) was 238 ppi, thepixel size was 106.5 μm×106.5 μm (35.5 μm×RGB×106.5 μm), and theaperture ratio was 56.0%. The reference sample 3 is a display panel witha gap spacer similarly to the sample 3. The reference sample 3 has astripe arrangement in which pixel electrodes of RGB subpixels arearranged in the same direction without being out of line. The referencesample 3 was fabricated by a method similar to that in Example 1 exceptthat a different photomask was used.

FIG. 31 shows an example of Id-Vg characteristics of the fabricatedtransistors. FIG. 31 shows the characteristics of channel-etchedtransistors using an In—Ga—Zn-based oxide as a semiconductor where achannel is formed. The transistor includes a first gate and a secondgate which are electrically connected to each other with a semiconductorprovided therebetween. The transistor has a channel width ofapproximately 3 μm and a channel length of approximately 3 μm.Measurement was performed under two conditions at the source-drainvoltages of 0.1 V and 20 V. The source-gate voltage was swept from −15 Vto 20 V. In addition, FIG. 31 shows field-effect mobility calculatedfrom data obtained when the source-drain voltage is 20 V. As seen fromFIG. 31, the transistors showed normally-off characteristics withextremely small variation. The highest field-effect mobility was as highas approximately 30 cm²/Vs.

FIG. 32A shows luminance dependence of NTSC ratio of each sample. Theresults of FIG. 32A show that the amount of change of NTSC ratio withrespect to the luminance is smaller in the samples 3 and 4 than in thereference sample 2.

FIG. 32B is a chromaticity diagram of each sample. The colorreproducibility of the samples 3 and 4 is improved as compared to thereference sample 2 as seen from FIG. 32B.

The above results show that each of the provision of a gap spacer andthe reduction in conductivity of an electron transport layer of alight-emitting element leads to enhancement of color reproducibility.

Next, the viewing angle dependence of chromaticity of the samples 3 and4 was measured. In measurement of the viewing angle dependence ofchromaticity, the direction perpendicular to the surface of the displaypanel was regarded as 0°, and the luminance spectra were measured atfive angles of −60°, −30°, 0°, 30°, and 60°. Then, the chromaticity ateach angle was calculated using the spectra. The luminance spectra weremeasured while the display panel displayed images of four colors of red,green, blue, and white. The viewing angle dependence of the chromaticitywas measured in two directions parallel to and perpendicular to thearrangement direction of the same color pixels of the display panel.

In addition, the viewing angle dependence of the chromaticity wasmeasured for the reference sample 3 at seven angles of −60°, −45°, −30°,0°, 30°, 45°, and 60°.

FIGS. 33A and 33B show the viewing angle dependence of chromaticity ofthe reference sample 3 and that of the sample 3, respectively. FIGS. 33Aand 33B show results of measurement in the direction perpendicular tothe arrangement direction of the same color pixels.

The horizontal axis and the vertical axis represent angle and the amountof change in chromaticity with reference to data at 0°, respectively.

As shown in FIG. 33B, a phenomenon in which the chromaticity changed asthe viewing angle increased was observed in the sample 3. In contrast,the change in the reference sample 3 was smaller than that in the sample3 as shown in FIG. 33A. In addition, the viewing angle dependence of thechromaticity in the direction parallel to the arrangement direction ofdifferent color pixels is particularly obvious. A cause of thephenomenon is considered that light emission from a light-emittingelement through a color filter of a pixel adjacent to the element easilyoccurs by an increase in distance between a light-emitting element and acolor filter due to a gap spacer. In addition, FIGS. 33A and 33B showthat the influence of a gap spacer on the viewing angle dependence isobvious in the extremely high-resolution display panel, whereas a gapspacer has little influence on the viewing angle dependence in thedisplay panel whose resolution is relatively low.

FIGS. 34A and 34B show measurement results of the viewing angledependence of the chromaticity of the sample 4. FIG. 34A shows resultsof measurement in the direction parallel to the arrangement direction ofthe same color pixels, and FIG. 34B shows results of measurement in thedirection perpendicular to the arrangement direction thereof.

As shown in FIGS. 34A and 34B, the viewing angle dependence of thechromaticity of the sample 4, in which the measure to reduce theconductivity of the electron transport layer of the light-emittingelement has been taken and did not include a gap spacer in order toreduce crosstalk, was significantly reduced as compared to the sample 3.

As a result of the measure to reduce the conductivity of an electrontransport layer of a light-emitting element, anextremely-high-resolution display panel having both high colorreproducibility and low viewing angle dependence of the chromaticity wasfabricated.

The above is the description of Example 3.

EXPLANATION OF REFERENCE

10: display device, 11: pixel portion, 12: circuit, 13: circuit, 14:circuit, 15 a: terminal portion, 15 b: terminal portion, 16 a: wiring,16 b: wiring, 16 c: wiring, 20: pixel unit, 21 a: pixel, 21 b: pixel,22: display region, 30 a: straight line, 30 b: straight line, 30 c:rectangle, 30 d: rectangle, 31: pixel electrode, 31 a: pixel electrode,31 b: pixel electrode, 32 a: pixel electrode, 32 b: pixel electrode, 33a: pixel electrode, 33 b: pixel electrode, 41 a: pixel circuit, 41 b:pixel circuit, 42 a: pixel circuit, 42 b: pixel circuit, 43 a: pixelcircuit, 43 b: pixel circuit, 51: wiring, 51 a: wiring, 51 b: wiring,52: wiring, 52 a: wiring, 52 b: wiring, 52 c: wiring, 52 d: wiring, 53S:wiring group, 53: wiring, 53 a: wiring, 53 b: wiring, 53 c: wiring, 54:wiring, 55: wiring, 57: wiring, 60: display element, 60 a: displayelement, 60 b: display element, 61: transistor, 62: transistor, 63:capacitor, 64: transistor, 71 a: subpixel, 71 b: subpixel, 72 a:subpixel, 72 b: subpixel, 73 a: subpixel, 73 b: subpixel, 80: circuit,81: transistor, 82: transistor, 83: wiring, 84: wiring, 85: terminal,86: output terminal, 91_1˜5: wiring, 92_1˜2: wiring, 93_1˜6: transistor,94: capacitor, 95: display element, 96_1˜3: wiring, 97_1˜3: wiring,98_1˜6: transistor, 101: substrate, 102: substrate, 211: insulatinglayer, 212: insulating layer, 213: insulating layer, 214: insulatinglayer, 215: spacer, 216: insulating layer, 220: adhesive layer, 221:insulating layer, 222: EL layer, 223: electrode, 224 a: opticaladjustment layer, 224 b: optical adjustment layer, 230 a: structure, 230b: structure, 231: light-blocking layer, 232 a: coloring layer, 232 b:coloring layer, 241: FPC, 242: FPC, 243: connection layer, 244: IC, 250:space, 251: transistor, 252: transistor, 253: conductive layer, 260:sealant 261: adhesive layer, 262: adhesive layer, 501: display portion,503 s: circuit, 505: touch panel, 509: FPC, 511: wiring, 519: terminalportion, 570: substrate, 590: substrate, 591: electrode, 592: electrode,594: wiring, 595: touch sensor, 597: adhesive layer, 598: wiring, 599:connection layer, 601: pulse voltage output circuit, 602: currentsensing circuit, 603: capacitor, 611: transistor, 612: transistor, 613:transistor, 621: electrode, 622: electrode, 901: housing, 902: housing,903: display portion, 904: display portion, 905: microphone, 906:speaker, 907: operation button, 908: stylus, 921: housing, 922: displayportion, 923: keyboard, 924: pointing device, 7000: display portion,7001: display portion, 7100: mobile phone, 7101: housing, 7103:operation button, 7104: external connection port, 7105: speaker, 7106:microphone, 7111: remote controller, 7200: television set, 7201:housing, 7203: stand, 7211: remote controller, 7300: portableinformation terminal, 7301: housing, 7302: operation button, 7303:information, 7304: information, 7305: information, 7306: information,7310: portable information terminal, 7320: portable informationterminal, 7400: lighting device, 7401: stage, 7402: light-emittingportion, 7403: operation switch, 7410: lighting device, 7412:light-emitting portion, 7420: lighting device, 7422: light-emittingportion, 7500: portable information terminal, 7501: housing, 7502:display portion tab, 7503: operation button, 7600: portable informationterminal, 7601: housing, 7602: hinge, 7650: portable informationterminal, 7651: non-display portion, 7700: portable informationterminal, 7701: housing, 7703 a: button, 7703 b: button, 7704 a:speaker, 7704 b: speaker, 7705: external connection port, 7706:microphone, 7709: battery, 7800: portable information terminal, 7801:band, 7802: input-output terminal, 7803: operation button, 7804: icon,7805: battery, 8000: camera, 8001: housing, 8002: display portion, 8003:operation button, 8004: shutter button, 8005: connection portion, 8006:lens, 8100: finder, 8101: housing, 8102: display portion, 8103: button,8200: head-mounted display, 8201: mounting portion, 8202: lens, 8203:main body, 8204: display portion, 8205: cable, 8206: battery, 9700:automobile, 9701: car body, 9702: wheels, 9703: dashboard, 9704: lights,9710: display portion, 9711: display portion, 9712: display portion,9713: display portion, 9714: display portion, 9715: display portion,9721: display portion, 9722: display portion, 9723: display portion.

This application is based on Japanese Patent Application serial no.2014-185978 filed with Japan Patent Office on Sep. 12, 2014, JapanesePatent Application serial no. 2014-218933 filed with Japan Patent Officeon Oct. 28, 2014, Japanese Patent Application serial no. 2014-242929filed with Japan Patent Office on Dec. 1, 2014, Japanese PatentApplication serial no. 2015-110198 filed with Japan Patent Office on May29, 2015, the entire contents of which are hereby incorporated byreference.

The invention claimed is:
 1. A display device comprising: a pixelcomprising a first subpixel, a second subpixel, and a third subpixel; afirst wiring; and a second wiring, wherein the first subpixel comprisesa first transistor and a first display element, wherein the secondsubpixel comprises a second transistor and a second display element,wherein the third subpixel comprises a third transistor and a thirddisplay element, wherein the first wiring is electrically connected to agate of the first transistor and a gate of the second transistor,wherein the second wiring is electrically connected to a gate of thethird transistor, wherein the first display element comprises a firstelectrode, wherein the second display element comprises a secondelectrode wherein the third display element comprises a third electrode,and wherein the third electrode is provided between the first electrodeand the second electrode, wherein the first electrode and the secondwiring are not overlapped with each other, wherein the second electrodeand the second wiring are not overlapped with each other, and whereinthe third electrode and the first wiring are overlapped with each other.2. The display device according to claim 1, wherein a straight linethrough a centroid of the first electrode and a centroid of the secondelectrode does not overlap with a centroid of the third electrode in aplane view.
 3. The display device according to claim 1, wherein aresolution is more than or equal to 400 ppi and less than or equal to2000 ppi.
 4. The display device according to claim 1, comprising acircuit, wherein the circuit has a function of selectively outputtingcurrent flowing through the first display element, and wherein thecircuit has a function of supplying a predetermined potential to thefirst display element.
 5. A display device comprising: a first pixelcomprising a first subpixel, a second subpixel, and a third subpixel; asecond pixel comprising a fourth subpixel, a fifth subpixel, and a sixthsubpixel; a first wiring; a second wiring; a third wiring; a fourthwiring; and a fifth wiring, wherein the first subpixel comprises a firsttransistor and a first display element, wherein the second subpixelcomprises a second transistor and a second display element, wherein thethird subpixel comprises a third transistor and a third display element,wherein the fourth subpixel comprises a fourth transistor and a fourthdisplay element, wherein the fifth subpixel comprises a fifth transistorand a fifth display element, wherein the sixth subpixel comprises asixth transistor and a sixth display element, wherein the first wiringis electrically connected to a gate of the first transistor, a gate ofthe second transistor, and a gate of the fourth transistor, wherein thesecond wiring is electrically connected to a gate of the thirdtransistor, a gate of the fifth transistor, and a gate of the sixthtransistor, wherein one of a source and a drain of the first transistoris electrically connected to the third wiring, wherein one of a sourceand a drain of the second transistor is electrically connected to thefourth wiring, wherein one of a source and a drain of the thirdtransistor is electrically connected to the third wiring, wherein one ofa source and a drain of the fourth transistor is electrically connectedto the fifth wiring, wherein one of a source and a drain of the fifthtransistor is electrically connected to the fourth wiring, and whereinone of a source and a drain of the sixth transistor is electricallyconnected to the fifth wiring.
 6. The display device according to claim5, wherein the first display element comprises a first electrode,wherein the second display element comprises a second electrode, whereinthe third display element comprises a third electrode, wherein thefourth display element comprises a fourth electrode, wherein the fifthdisplay element comprises a fifth electrode, wherein the sixth displayelement comprises a sixth electrode, wherein the third electrode isprovided between the first electrode and the second electrode, whereinthe fourth electrode is provided between the fifth electrode and thesixth electrode, and wherein the second electrode is adjacent to thefifth electrode.
 7. The display device according to claim 6, wherein acentroid of the first electrode, a centroid of the second electrode, anda centroid of the fourth electrode are in a first line, wherein acentroid of the third electrode, a centroid of the fifth electrode, anda centroid of the sixth electrode are in a second line, and the firstline is parallel to and does not overlap with the second line.
 8. Thedisplay device according to claim 6, wherein the first electrode and thesecond wiring are not overlapped with each other, wherein the secondelectrode and the second wiring are not overlapped with each other,wherein the third electrode and the first wiring are overlapped witheach other wherein the fourth electrode and the second wiring are notoverlapped with each other, wherein the fifth electrode and the firstwiring are overlapped with each other, and wherein the sixth electrodeand the first wiring are overlapped with each other.
 9. The displaydevice according to claim 5, wherein the first display element and thefifth display element have a function of emitting light of a firstcolor, wherein the second display element and the sixth display elementhave a function of emitting light of a second color, and wherein thethird display element and the fourth display element have a function ofemitting light of a third color.
 10. The display device according toclaim 5, wherein a resolution is more than or equal to 400 ppi and lessthan or equal to 2000 ppi.
 11. The display device according to claim 5,comprising a circuit, wherein the circuit has a function of selectivelyoutputting current flowing through the first display element, andwherein the circuit has a function of supplying a predeterminedpotential to the first to third display element.
 12. A display devicecomprising: a first pixel comprising a first subpixel, a secondsubpixel, and a third subpixel; a first wiring; and a second wiring,wherein the first subpixel comprises a first transistor and a firstdisplay element comprising a first electrode, wherein the secondsubpixel comprises a second transistor and a second display elementcomprising a second electrode, wherein the third subpixel comprises athird transistor and a third display element comprising a thirdelectrode, wherein the first wiring is electrically connected to a gateof the first transistor and a gate of the second transistor, wherein thesecond wiring is electrically connected to a gate of the thirdtransistor, wherein the first electrode, the second electrode, and thethird electrode are along a first direction parallel to the firstwiring, wherein the first transistor and the second transistor are alongthe first direction, and wherein the first transistor and the thirdtransistor are along a second direction perpendicular to the firstwiring.
 13. The display device according to claim 12, wherein the thirdelectrode is provided between the first electrode and the secondelectrode.
 14. The display device according to claim 12, furthercomprising: a second pixel comprising a fourth subpixel, a fifthsubpixel, and a sixth subpixel; wherein the fourth subpixel comprises afourth transistor and a fourth display element comprising a fourthelectrode, wherein the fifth subpixel comprises a fifth transistor and afifth display element comprising a fifth electrode, wherein the sixthsubpixel comprises a sixth transistor and a sixth display elementcomprising a sixth electrode, wherein the first wiring is electricallyconnected to the gate of the first transistor, the gate of the secondtransistor, and a gate of the fourth transistor, wherein the secondwiring is electrically connected to the gate of the third transistor, agate of the fifth transistor, and a gate of the sixth transistor, andwherein the fourth electrode, the fifth electrode, and the sixthelectrode are along the first direction.
 15. The display deviceaccording to claim 14, wherein the first transistor, the secondtransistor, and the fourth transistor are along the first direction,wherein the third transistor, the fifth transistor, and the sixthtransistor are along the first direction, wherein the first transistorand the third transistor are along the second direction, wherein thesecond transistor and the fifth transistor are along the seconddirection, and wherein the fourth transistor and the sixth transistorare along the second direction.
 16. A display device comprising: a pixelcomprising a first subpixel, a second subpixel, and a third subpixel; afirst wiring; a second wiring; a third wiring; and a fourth wiring,wherein the first subpixel comprises a first transistor and a firstdisplay element, wherein the second subpixel comprises a secondtransistor and a second display element, wherein the third subpixelcomprises a third transistor and a third display element, wherein thefirst wiring is electrically connected to a gate of the first transistorand a gate of the second transistor, wherein the second wiring iselectrically connected to a gate of the third transistor, wherein thethird wiring is electrically connected to one of a source and a drain ofthe first transistor and one of a source and a drain of the thirdtransistor, and wherein the fourth wiring is electrically connected toone of a source and a drain of the second transistor.
 17. The displaydevice according to claim 16, wherein the first display element can emitlight of red color, wherein the second display element can emit light ofblue color, and wherein the third display element can emit light ofgreen color.
 18. The display device according to claim 16, wherein thefirst transistor and the second transistor are arranged in a firstdirection which is parallel to the first wiring, and wherein the firsttransistor and the third transistor are arranged in a second directionwhich is parallel to the third wiring.
 19. The display device accordingto claim 16, wherein a resolution is more than or equal to 400 ppi andless than or equal to 2000 ppi.
 20. The display device according toclaim 16, comprising a circuit, wherein the circuit has a function ofselectively outputting current flowing through the first displayelement, and wherein the circuit has a function of supplying apredetermined potential to the first display element.